International armed conflict in Ukraine

For an international armed conflict (IAC) to exist, there must have been a resort to armed force involving at least two states. The threshold for an IAC is very low and does not require a certain intensity or duration. The existence of an international armed conflict is to be determined by the facts, not the subjective intent of the belligerents. For further information, see the Classification section.

February 2014 – February 2022

Following the protests of Euromaidan and the consequent fall of the Ukrainian president Viktor Yanukovich in February 2014, Russian soldiers without distinctive insignias allegedly arrived in Crimea, took control of strategic positions, and captured the parliament in Crimea. ‘From 'Not Us' To 'Why Hide It?': How Russia Denied Its Crimea Invasion, Then Admitted It’, Radio Free Europe Radio Liberty, 26 February 2019. In April, concurrent Anti-Maidan demonstrations held by pro-Russian separatists in Donbass (east Ukraine) turned into armed confrontations with the Ukrainian armed forces. After capturing local government buildings, the separatists declared the creation of Donetsk and Luhansk People’s Republics. ‘Armed pro-Russian insurgents in Luhansk say they are ready for police raid’, Kyiv Post, 12 April 2014.

From the outset, Ukraine has consistently claimed that Russian soldiers were participating in the fighting in eastern Ukraine. However, Russia has denied these allegations, claiming that the Russians fighting in Ukraine are volunteers, including discharged members of the Russian army. ‘Ukraine Crisis: Thousands of Russian Fighting in East’, BBC, 28 August 2014, M. Urban, ‘How Many Russians Are Fighting in Ukraine?’, BBC, 10 March 2015. Ukraine has repeatedly captured Russian servicemen in eastern Ukraine. 'Captured Russian Troops "in Ukraine by Accident", BBC, 26 August 2014; A. Luhn, 'Russian Soldiers Captured in Ukraine to Face Trial on Terrorism', The Guardian, 18 May 2015. Locals have also repeatedly claimed that Russian soldiers were fighting alongside rebels. S. Walker, A. Luhn, 'Tension High in Ukrainian Border Towns Menaced by Russian Forces', The Guardian, 30 August 2014. In July 2014, Ukraine accused Russia of having shot down a Ukrainian military plane. 'Ukraine Conflict: Russia Accused of Shooting Down Jet, BBC, 17 July 2014. Both have accused each other of cross-border shelling. 'Ukraine and Russia Claim Cross Border Fire', Al-Jazeera, 25 July 2014. Based on the analysis of satellite images and social media, there has been evidence of crossborder artillery shelling since 14 July 2014. Bellingcat, Origin of Artillery Attacks on Ukrainian Military Positions in Eastern Ukraine between 14 July 2014 and 8 August 2014, 15 January 2015; S. Case, Putin's Undeclared War: Summer 2014 - Russian Artillery Strikes Against Ukraine, Bellingcat, 21 December 2016; S. Frizell, 'U.S: Satellite Imagery Shows Russian Shelling Easter Ukraine, Time, 27 July 2014. Finally, there have been many reports of Russian soldiers having died in Ukraine. O. Boldyrev, 'Ukraine Conflict: Russian Families Look For Soldier Sons', BBC, 28 August 2014; A. Luhn, 'They were Never There: Russia's Defence for Families of Troops Killed in Ukraine', The Guardian, 19 January 2015.

While at the beginning of 2014 Russian President Putin claimed that the armed forces participating in the capture of the Verkhovna Rada of the Autonomous Republic of Crimea were local forces, in November 2014 he openly acknowledged that the Russian army participated in the annexation of Crimea. ‘Путин признал, что российская армия блокировала украинскую в Крыму’, Украинская правда, 17 November 2014. Furthermore, in December 2015, President Putin admitted the presence of Russian military specialists in Eastern Ukraine. During a press conference, after being asked about the capture of two Russian military intelligence officers in Ukraine, the Russian President conceded that there are Russian officers operating in the country: ‘[w]e never said there were not people there who carried out certain tasks including in the military sphere.’ Nevertheless, he stressed that this was ‘not the same as regular Russian troops.’ ‘Putin admits Russian military presence in Ukraine for first time’, The Guardian, 17 December 2015.

On 25 November 2018, three Ukrainian Navy vessels were fired upon and then captured by the Russian Federal Security Service (FSB) when they attempted to pass from the Black Sea into the Sea of Azov heading towards the port of Mariupol. 24 Ukrainians were captured and sent to prison to Moscow. According to the 2003 Treaty between the Russian Federation and Ukraine on Cooperation in the Use of the Sea of Azov and the Kerch Strait, the strait and the Azov sea are intended to be shared waters between the two states. Nevertheless, Russia claims that Ukraine should ask permission before entering the waters along the Crimean perimeter. Following the incident, the Ukrainian President Petro Poroshenko declared martial law along the Ukrainian border with Russia, which was approved by the Parliament and lasted until 26 December 2018. ‘The Kerch Strait incident’, International Institute for Strategic Studies (IISS).

The United Nations General Assembly (UNGA) adopted a resolution on the matter, titled ‘The problem of militarization of the Autonomous Republic of Crimea and the city of Sevastopol (Ukraine), as well as parts of the Black Sea and the Sea of Azov’, where it called for the release of Ukraine’s vessels and crew members Russia captured. Furthermore, it condemned ‘the construction and opening of the Kerch Strait bridge between the Russian Federation and temporarily occupied Crimea, which facilitates the further militarization of Crimea’ and ‘the increasing military presence of the Russian Federation in parts of the Black Sea and the Sea of Azov, including the Kerch Strait, and the Russian Federation’s harassment of commercial vessels and restriction of international shipping there.’ UNGA, Problem of the militarization of the Autonomous Republic of Crimea and the city of Sevastopol, Ukraine, as well as parts of the Black Sea and the Sea of Azov, UN Doc. A/73/L.47, 5 December 2018.

On 16 September 2016, Ukraine instituted arbitral proceedings against Russia under Part XV and Annex VII of the 1982 United Nations Convention on the Law of the Sea (UNCLOS). On 25 May 2019, the International Tribunal for the Law of the Sea (ITLOS) adopted provisional measures. Specifically, it required ‘the Russian Federation to release the three Ukrainian naval vessels and the 24 detained Ukrainian servicemen and to allow them to return to Ukraine in order to preserve the rights claimed by Ukraine.’ However, it did not consider it necessary to require the Russian Federation to suspend criminal proceedings against the 24 detained Ukrainian servicemen and refrain from initiating new proceedings.’ On the other hand, it ordered ‘both Parties to refrain from taking any action which might aggravate or extend the dispute submitted to the Annex VII arbitral tribunal.’ ITLOS, Case Concerning the Detention of Three Ukrainian Naval Vessels (Ukraine v Russian Federation), Request for the prescription of provisional measures, Order, No. 26, 25 May 2019, §§118-119.

All these factors combined point towards direct Russian involvement in eastern Ukraine, directly in hostile encounters with Ukrainian forces and in support of the rebels since July 2014. Hence, in addition to the non-international armed conflicts between the rebels and the government that were ongoing at the time, there was a parallel international armed conflict between Ukraine and Russia.

Nevertheless, it is worth noting that at the time the Russian involvement did not turn the NIAC between Ukraine and the self-proclaimed ‘People’s Republics’ of Donetsk and Lubansk into an IAC. As clarified by the International Criminal Tribunal for the Former Yugoslavia (ICTY) in its seminal Tadic decision, ‘in order to attribute the acts of a military or paramilitary group to a State, it must be proved that the State wields overall control over the group, not only by equipping and financing the group, but also by coordinating or helping in the general planning of its military activity.’ ICTY, The Prosecutor v Duško Tadic, Appeals Chamber, Judgment, IT-94-1-A, 25 July 1999, §131. For further information on the question of control, see the Classification section While evidence suggested that Russia was training and equipping the armed groups and providing them with weapons, M.R. Gordon, ‘Russia Continues to Train and Equip Ukraine Rebels, NATO Official Says’, The New York Times, 4 November 2014. This did not amount to overall control per se: as aforementioned, ‘coordinating or helping in the general planning of its military activity’ are also required to make IHL of international armed conflicts exclusively applicable. ICTY, The Prosecutor v Duško Tadic, Appeals Chamber, Judgment, IT-94-1-A, 25 July 1999, §131. Accordingly, at the time it was not possible to conclude with a degree of certainty that Russia was exercising overall control over the opposition groups operating in Ukraine. The situation changed in Spring 2022, as Russia started exercising overall control over the separatist groups, hence turning the NIACs into an IAC.

Invasion of Ukraine from February 2022

In 2021, tensions between Russia on the one hand and Ukraine and a number of western countries on the other have escalated. Since US President Biden took office in January 2021, Ukrainian President Volodymyr Zelensky adopted a more assertive strategy vis-à-vis Russia, while starting a discussion regarding the possibility to join NATO. As a reaction, Putin started deploying Russian troops at the Ukrainian border. On the other hand, on 26 October 2021, Ukraine ‘destroyed a D-30 howitzer used by Russian-backed separatists in the eastern Donbas region’ using a Turkish drone. Furthermore, in November US warships were found sailing in the Black Sea, while satellite imagery showed an increased number of Russian troops close to the border with Ukraine. In December, Biden announced that Western countries would adopt sanctions against Russia, should it invade Ukraine, while Putin demanded that Western countries and NATO cease all military activities close to Ukraine and that the latter will not be accepted as member of NATO. In January and February 2022, diplomatic attempts to de-escalate proved unsuccessful. L. Ragozin, ‘Russia-US escalation: How did we get here?’, Al Jazeera, 21 December 2021; ‘Timeline: How did the recent Ukraine-Russia crisis start?’, Al Jazeera, 13 February 2022; I. Khurshudyan and D. L. Stern, ‘Why Ukraine’s Turkish-made drone became a flash point in tensions with Russia’, The Washington Post, 15 January 2022;  ‘U.S. navy ship tracked by Russia on entry to Black Sea’, Reuters, 4 November 2021.

On 21 February 2022, Putin formally recognized independence of separatist regions in eastern Ukraine. In a televised announcement, he affirmed that ‘I deem it necessary to make a decision that should have been made a long time ago – to immediately recognize the independence and sovereignty of the Donetsk People’s Republic and the Luhansk People’s Republic.’ In the meantime, Putin deployed more troops to the border with Ukraine. The day after, Russian President ordered troops to enter easter Ukraine and claimed that they have a peacekeeping function. ‘Ukraine crisis: Russia orders troops into eastern Ukraine’, BBC, 22 February 2022; ‘Putin recognises independence of Ukraine breakaway regions’, Al Jazeera, 22 February 2022.

On 24 February 2022, Russian forces entered Ukraine and began targeting military objectives close to the major Ukrainian cities. During the following hours, airstrikes continued and extended to other areas of Ukraine, including the capital Kyiv. Attacks started being conducted against civilians too. For instance, it has been reported that an apartment complex outside of Kharkiv – one of the main cities of Ukraine – was directly targeted. On 25 February, rocket strikes have hit Kyiv, while Russian tanks have been seen approaching the capital. At least 660,000 people have been displaced and sought refuge in neighbouring countries and the EU, by the end of the month. ‘Ukraine conflict: Simple visual guide to the Russian invasion’, BBC, 25 February 2022; ‘Ukraine slams ‘horrific’ strikes on Kyiv amid Russian advance’, Al Jazeera, 25 February 2022; International Crisis Group, Crisis Watch, February 2022. These numbers have risen dramatically and the UN reports about 7 million internally displaced persons and 6,5 million people seeking refuge outside of Ukraine. In addition, about 13 million people are unable to flee the areas affected by hostilities. ‘Ukraine emergency’, UNHCR; ‘Refugees from Ukraine across Europe’, UNHCR, 19 May 2022.

Since entering Ukrainian territory, Russian troops have remained militarily active on a large scale. By the beginning of March 2022, almost all of the 190,000 Russian troops deployed on the border were operative on Ukrainian territory, in the north, south and east. Christina Wilkie, ‘Nearly all of Russia’s initial invasion forces now in Ukraine, Pentagon says’, CNBC, 7 March 2022; Mark F. Cancian, ‘Russian Casualties in Ukraine: Reaching the Tipping Point’, Center for Strategic and International Studies, 31 March 2022. Ukraine, in turn, had an army of 126,000 when the Russians entered Ukraine. Ukraine, however, receives international support from NATO countries in the form of military intelligence and supplies. Alex Gatopoulos, ‘Total war: How Ukraine mobilized a country as Russia overreached’, Al Jazeera, 9 March 2022; Henry Sandercock, ‘Russia-Ukraine war: how big is Ukraine’s army - size of armed forces compared to Russia, UK, US, NATO’, National World, 20 May 2022. In this regard, it may be noted, for example, that the Ukrainian attack that resulted in the sinking of Russia's flagship Black Sea missile cruiser 'Moskva' on 14 April 2022, is reported to have been carried out with the assistance of US intelligence. ‘Moskva sinking: US gave intelligence that helped Ukraine sink Russian cruiser – reports’, BBC News, 6 May 2022.

During the second phase of the invasion, that went from March to June 2022, Russia focused on eastern Ukraine, while Ukrainian troops engaged in counter-offensives in the north and south of the country. In the meantime, the UK and US provided advanced missile systems to Ukraine. ‘Timeline: Six months of Russia’s war in Ukraine’, al Jazeera, 24 August 2022. During those months, the main center of Russian military activity was the port city of Mariupol in the Donbas region. Russia besieged this city because it was Ukraine's last stronghold to prevent total Russian control of the Black Sea coast. For Russia, this was crucial in order to create a land bridge to occupied Crimea and in a later phase capture Odessa to cut off Ukraine’s access to the Black Sea. Reportedly, around 170,000 people were besieged, and 90 percent of the city was destroyed as of late March. Frank Gardner, ‘Mariupol; Why Mariupol is so important to Russia’s plan’, BBC News, 21 March 2022; Max Hunder, ‘Timeline: Russia’s siege of the Ukrainian city of Mariupol’, Reuters, 30 March 2022; International Crisis Group, Crisis Watch, March 2022. In the Azovstal steel plant in Mariupol, Ukrainian armed forces hided in order to defend the city and vowed to fight until the end. ‘Ukrainian fighters at besieged Azovstal plant vow to fight till the end’, Reuters, 8 May 2022; ‘Azovstal defenders vow to fight until the end, saying, ‘we don’t have much time’’, RFE/RL’s Ukrainian Service, 8 May 2022. Due to the worsening humanitarian situation, the situation in Mariupol was explicitly part of the talks between UN Secretary-General Guterres and President Putin, when the former visited Moscow to discuss the war on 26 April 2022. ‘Russia agrees ‘in principle’ to UN and Red Cross involvement in evacuations from Mariupol’, UN News, 26 April 2022. By that time, around 100,000 people, including an estimated 2,000 Ukrainian armed forces in the Azovstal steel plant, remained under the Russian siege. On 30 April, evacuations of civilians trapped in the steel plant started after which the remaining Ukrainian forces were ordered on 20 May 2022 to withdraw and surrender. This ended one of the most destructive sieges of the war so far. ‘Russia-Ukraine war: ‘Safe passage operation’ starts in Mariupol’, Al Jazeera, 1 May 2022; ‘Another 40 people evacuated from territory of Azovstal plant in Mariupol’, Tass, 1 May 2022; ‘50 more civilians rescued from besieged steel plant in Mariupol’, Al Jazeera, 6 May 2022; Oleksiy Sorokin, ‘264 Azovstal defenders evacuated to Russian-controlled territory, promised medical treatment’, Kyiv Independent, 17 May 2022; ‘War in Ukraine: Kyiv orders Azovstal troops to stop fighting, Russia claims control of Mariupol’, Le Monde, 20 May 2022; ‘Siege ends at Ukraine’s Mariupol steelworks, Russia seeks control of Donbas’, Euractiv, 21 May 2022; ‘Russian soldiers start clearing mines from Ukraine’s Azovstal’, Reuters, 23 May 2022.

July 2022 marked the beginning of a new phase of the conflict, as Russia focused on taking control over Kherson and Zaporizhia in the south. On 22 June, Russia and Ukraine signed an agreement brokered by the UN which lifted Russian blockade and allowed the exportation of grain from Ukraine through the Black Sea. The first ship loaded with Ukrainian grain left on 22 July. On 9 August, Ukraine launched its first significant attack against a Russian base in Crimea, which destroyed 9 Russian warplanes. Another attack led to the destruction of a Russian ammunition warehouse in Crimea. Furthermore, in September Ukraine recaptured a substantial part of the northeastern Kharkiv region. M. M. Bigg, ‘Russia invaded Ukraine more than 200 days ago. Here is one key development from every month of the war’, The New York Times, 13 September 2022; ‘Timeline: Six months of Russia’s war in Ukraine’, al Jazeera, 24 August 2022.

On 9 November 2022, Stremousov, the Russian administrator of Kherson, was reportedly killed in a car crash. On the same day, Russia ordered its troops to withdraw from the key city of Kherson, which was the only regional capital captured by the invading forces since February 2022. Russian General Sergey Surovikin explained in a televised announcement that it was no longer possible to keep Kherson city supplied. ‘Russia orders troop withdrawal from Ukraine’s Kherson city’, Al Jazeera, 9 November 2022; P. Kirby, F. Gardner, J. Bowen, ‘Kherson: Russia to withdraw troops from key Ukrainian city’, BBC, 9 November 2022; ‘Timeline: Key developments in Ukraine’s Kherson since invasion’, Al Jazeera, 9 November 2022. Following an eight-month battle, on 21 May 2023 President Zelenzkyy announced that Wagner group, with Russian troops, completely destroyed the city of Bakhmut. While a number of Russian sources affirm that the city has fallen into Russian hands, Ukraine has denied such claims. ‘Russians ‘destroyed everything’ in Bakhmut: Ukraine’s Zelenskyy’, Al Jazeera, 21 May 2023; ‘Putin congratulates Russia troops, Wagner for ‘capturing Bakhmut’, Al Jazeera, 21 May 2023.

On 3 May 2023, Russia accused Ukraine of having attempted to kill President Putin in Moscow. Notably, a footage showed a drone attack over the Kremlin in the capital. Ukrainian President Zelenskiy affirmed that Ukraien is not responsible for the attack and reiterated that Ukrainian forces only fight on their territory, not on Russian soil. Official Russian sources have confirmed that ‘as a result of timely actions taken by the military and special services with the use of radar warfare systems, the devices were put out of action.’ A few weeks later, on 30 May 2023, drone strikes hit Moscow. The mayor of the capital, Sergei Sobyanin, affirmed that two people were injured and that residents in two apartment blocks were evacuated. ‘Ukraine tried to assassinate Putin by drone, Kremlin says’, Reuters, 3 May 2023; ‘Russia accuses Ukraine of attempt to kill Putin with drones’, Al Jazeera, 3 May 2023; ‘Drone attacks hit Moscow, sparking fury at the Kremlin’, Al Jazeera, 30 May 2023.

Since the first months of 2023, two Russian paramilitary groups based in Ukraine – the Liberty of Russia Legion (LSR) and the Russian Volunteer Corps (RDK) – have carried out a cross-border raid against Russia. The first attack on Russian soil was reported on 3 March, when armed clashes took place in Suchani and Lyubechan, two villages of the Bryansk region, close to the Ukrainian border. On 22 May 2023, LSR and RDK carried out new attacks against Russia, in some border villages in the Belgorod region. While at first they gained contol over some of these towns, they had to retreat soon thereafter. The two groups are based in Ukraine and receive from the state intelligence, fuel, food and medicine. However, it seems that Ukraine’s help do not go as far as providing weapons or other war materiel. B. Vitkine, ‘Russia reports fighting on its territory for the first time’, Le Monde, 3 March 2023; ‘Belgorod: Russian paramilitary group vows more incursions’, BBC News, 22 May 2023. According to the ICTY, ‘in order to attribute the acts of a military or paramilitary group to a State, it must be proved that the State wields overall control over the group, not only by equipping and financing the group, but also by coordinating or helping in the general planning of its military activity. Only then can the State be held internationally accountable for any misconduct of the group.’ Therefore, it seems not possible to attribute the actions of these groups to Ukraine. ICTY, Prosecutor v. Dusko Tadić, Judgment, Appeals Chamber (IT-94-1) 15 July 1999, §131. In light of the number of confrontations, the intensity of violence does not seem enough to conclude that there is a NIAC between the paramilitary groups and Russia. 

On 6 June 2023, a major hydroelectric dam on the Dnipro River was destroyed, causing an ecological disaster and focing thousand of people to flee their homes. Ukraine accused Russia of destroying the dam, which was in an area under the control of Russian forces. President Zelenskiy wrote on twitter that ‘it is physically impossible to blow it up somehow from the outside, by shelling. It was mined by the Russian occupiers. And they blew it up.’ On the other had, Russia has accused Ukraine of the destruction of the dam. D. Sabbagh and J. Borger, ‘Thousands flee homes as collapse of dam is blamed on Russian forces’, The Guardian, 6 June 2023; ‘Ukraine, Russia trade blame for destruction of Nova Kakhovka dam’, Al Jazeera, 6 June 2023.

IAC by proxy

In the aftermath of the occupation of Crimea by Russia, protests in the Luhansk and Donetsk provinces in Donbass, a region in eastern Ukraine, turned into non-international armed conflicts in spring 2014.

Since the beginning of 2022, Russia has increasingly played a crucial role in coordinating and planning military actions of the separatist armed forces. There are a number of elements that suggest that Russia exercises overall control over the separatists. First, Russian officers and personnel have been transferred to the political and military composition of the DPR and LPR forces. It has been proven that officials from the Federal Security Service (FSB) and from the Main Intelligence Directorate (GRU) were transferred into DPR and LDP law enforcement agencies with key roles, while Russian Federation Air Force (RFAF) officers and servicemen were also sent to the Ukrainian 8th Army Corps as well as into the structures of the 1st and 2nd Army Corps; Russia was also involved in the recruitment and deployment of Russian mercenaries and volunteers to join the DPR and LPR forces. Global Rights Compliance, ‘International Law and Defining Russia’s Involvement in Crimea and Donbas’, 13 February 2022; Pavle Kilibarda, ‘Was Russia’s Recognition of the Separatist Republics in Ukraine ‘Manifestly’ Unlawful?’, EJIL: Talk!, 2 March 2022. This has allowed  Russia to influence the decision-making process of the separatist armed groups. Since then, Russia has thus played a crucial role in the planning and coordination of the activities of the DPR and LPR forces, which also corresponded to Russian military objectives. Natia Kalandarishvili-Mueller, 'Russia's "Occupation by Proxy" of Eastern Ukraine - Implications Under the Geneva Conventions’, Just Security, 22 February 2022. In addition, it has also been proven that DPR and LPR armed forces received direct orders and instructions during different operations coming from Russian forces. Andrey Goryanov, Olga Ivshina, ‘DPR special forces fighter: Russia's aid was decisive’, BBC, 31 March 2015; Bellingcat, ‘Russian Officers and Militants Identified as Perpetrators of the January 2015 Mariupol Artillery Strike’, 2018, p.12; ‘Social networks claim that a Russian general is commanding militants in Debaltseve’, Ukrainska Pravda, 18 February 2015. It seems important to remind that it is not required that each and every operation shall be directed by the controlling State for the overall control to be established. ICTY, The Prosecutor v Duško Tadić, Appeals Chamber, Judgment, IT-94-1-A, 25 July 1999, §137.

Russia has exercised its control over the separatists at the political level, inasmuch as it appointed curators and has approved members of the DPR and LPR governments, leading Russia to be able to control the structures and politics of the DPR and LPR. Vladimir Peshkov, ‘The Donbas: Back in the USSR’, European Council on Foreign Relations, 1 September 2016; Anton Zverev, ‘Ex-rebel leaders detail role played by Putin aide in east Ukraine’, Reuters, 11 May 2017; ‘MH17 Witness Appeal November 2019’, Politie. Furthermore, the DPR and LPR economically depend on Russia. This therefore not only permits the delivery of artillery fire from Russia but also the payment of the salaries for example. Julian Röpcke, ‘How Russia finances the Ukrainian rebel territories’, Bild, 16 January 2016; ‘Refusal to pay pensions to residents of Donbass explained by their pro-Russian sentiments’, Lenta, 5 February 2020; Donald N. Jensen, Moscoww in the Donbass: Command, Control, Crime and the Minsk Peace Process, NATO Defense College, 2017. 

In light of the foregoing, it is possible to conclude that Russia exercises overall control over the DPR and LPR separatist armed groups and therefore the separatist groups can be considered as de facto organs of Russia. Indeed, as clarified by the International Criminal Tribunal for the Former Yugoslavia (ICTY): ‘in order to attribute the acts of a military or paramilitary group to a State, it must be proved that the State wields overall control over the group, not only by equipping and financing the group, but also by coordinating or helping in the general planning of its military activity.’ ICTY, The Prosecutor v. Dusko Tadić, Appeal Chamber Judgment, 15 July 1999, §131. Accordingly, the NIAC between such groups and Ukraine turned into an IAC between Russia and Ukraine in Spring 2022.

Referendum in September 2022

During the last week of September 2022, referendums took place in four Ukrainian regions occupied by Russia, namely Luhansk, Donetsk, Kherson and Zaporizhzhia. Residents of some of these areas have reported that Russian soldiers went door to door to encourage people to vote. On 28 September, Kremlin-installed governments of the four Russian-occupied areas of Ukraine announced that the majority of residents voted in favour of joining Russia. On Friday, 30 September, President Putin unlawfully annexed these territories to the Russian Federation. ‘Annexation announcement follows so-called referendums’, BBC News, 30 September 2022; ‘Ukraine 'referendums': Full results for annexation polls as Kremlin-backed authorities claim victory’, Euronews, 28 September 2022.

Since these regions are occupied by Russia, the law of occupation is applicable. Notably, the occupying power does not gain sovereignty over the occupied territory: the rationale underpinning the law of occupation is that the occupying territory is held in trusteeship until the lawful sovereign returns.  Therefore, holding referendums to annex these areas is unlawful. E. Lieblich, ‘Q&A on Russia-Backed Referendums in Eastern Ukraine and International Law’, Just Security, 24 September 2022.

Missile fired against Poland

On 15 November 2022, a missile fell on the Polish village of Przewodow, at the border with Ukraine, killing two individuals. While Poland claimed that the missile was Russian, Biden said that it is unlikely that it was fired from Russia. Initial findings would suggest the the missile was fired by Ukrainian forces at an incoming Russian missile. According to the head of the permanent mission of Russia to the United Nations, this ‘is an attempt to provoke a direct military clash between NATO and Russia, with all the consequences for the world.’ M. Gadzo, ‘Poland blast an attempt to spark NATO-Russia clash – Moscow’, Al Jazeera, 16 November 2022; ‘Explosion in Poland Kills Two Near Border With Ukraine’, The New York Times, 16 November 2022; ‘Russia-Ukraine war live: China and France urge calm and caution after missile kills two in Poland’, The Guardian, 16 November 2022; ‘Ukraine war: Russia denies responsibility for Poland blast’, BBC, 16 November 2022.

It should be noted that the situation is evolving rapidly as the IAC between Russia and Ukraine is still ongoing.

International Criminal Court (ICC)

In November 2016, the Office of the Prosecutor of the International Criminal Court concluded in its Report on Preliminary Examination Activities that the available information 'would suggest the existence of an international armed conflict in the context of armed hostilities in eastern Ukraine from 14 July 2014 at the latest, in parallel to the non-international armed conflict.' Office of the Prosecutor, Report on Preliminary Examination Activities, November 2016, §169. For a contrary view, albeit reached at an earlier point in time, see R. Heinsch, ‘Conflict Classification in Ukraine’, International Law Studies 91 (2015), U.S. Naval College of War, p 354.

On 28 February 2022, ICC Prosecutor Karim Asad Ahmad Khan QC declared to open an investigation on his own motion into the situation in Ukraine. Karim Asad Ahmad Khan QC, ‘Statement of ICC Prosecutor, Karim A.A. Khan QC, on the situation in Ukraine: “I have decided to proceed with opening an investigation”’, Office of the Prosecutor, 28 February 2022. Ukraine is not a state party to the Rome Statute, but they have lodged two declarations in conformity with art 13 (3) Rome Statute in order to accept the ICC’s jurisdiction over crimes of the Rome Statute occurring on their territory. The first statement indicates the starting date of Ukraine's acceptance of ICC jurisdiction, i.e. 21 November 2013. ‘Declaration of 9 April 2014 accepting jurisdiction of the ICC’, Embassy of Ukraine, 9 April 2014. The second declaration of 8 September 2015 expressly accepted jurisdiction for an indefinite duration. Pavlo Klimkin (Minister of foreign affairs), ‘Declaration of 8 September 2015 accepting jurisdiction of the ICC’, 8 September 2015.

The investigation concerns all crimes stipulated in the Rome Statute committed by any person from 21 November 2013 onwards. However, there is no ground for investigations over the crime of aggression because the officials that could be prosecuted for having committed this crime are of a nationality that is not a party to the Rome Statute. Moreover, there is also no UNSC referral which could have circumvented this obstacle. Sergey Vasiliev, ‘Aggression against Ukraine: Avenues for Accountability for Core Crimes’, EJIL Talk!, 3 March 2022. On 2 March 2022, the Prosecutor announced that 39 state parties made a referral of the situation to the Prosecutor’s Office. Karim Asad Ahmad Khan QC, ‘Statement of ICC Prosecutor, Karim A.A. Khan QC, on the Situation in Ukraine: Receipt of Referrals from 39 States Parties and the Opening of an Investigation’, Office of the Prosecutor, 2 March 2022. Meanwhile, Japan, North Macedonia, Montenegro, and Chile also referred the situation to the Prosecutor’s office. These referrals allow the Prosecutor to open an investigation immediately, without the preliminary hurdle of obtaining the authorization of the Pre-Trial Chamber of the Court. The investigation is ongoing and, on 17 May 2022, the Prosecutor announced that a 42-member team of experts was sent to Ukraine to investigate on the crimes falling within the ICC’s jurisdiction. ‘ICC sends 42-member team to probe alleged war crimes in Ukraine’, Al Jazeera, 17 May 2022; Karim A.A. Khan QC, ‘ICC Prosecutor Karim A.A. Khan QC announces deployment of forensics and investigative team to Ukraine, welcomes strong cooperation with the Government of the Netherlands’, Office of the Prosecutor, 17 May 2022.

It should be noted that a number of scholars are suggesting the establishment of an ad hoc tribunal to investigate and prosecute the crime of aggression allegedly committed by certain political and military leaders of the Russian Federation. Gordon Brown, Dapo Akande, Mykola Gnatovsky, Murray Hunt and others, ‘Combined Statement and Declaration calling for the creation of a Special Tribunal for the Punishment of the Crime of Aggression Against Ukraine, 4 March 2022; Ewelina U. Ochab, ‘Experts call for the creation of a special tribunal for the punishment of the crime of aggression against Ukraine’, Forbes, 4 March 2022; Tom Dannenbaum, ‘Mechanisms for criminal prosecution of Russia’s aggression against Ukraine’, Just Security, 10 March 2022. For instance, the Parliamentary Assembly of the Council of Europe passed a resolution in this respect, urging all member states to set up such a criminal tribunal. ‘PACE calls for an ad hoc international criminal tribunal to hold to account perpetrators of the crime of aggression against Ukraine’, Council of Europe, 28 April 2022. However, not everyone is in favour of this idea and questions are raised about the suitability of such a mechanism. Sergey Vasiliev, ‘Aggression against Ukraine: Avenues for Accountability for Core Crimes’, EJIL Talk!, 3 March 2022; Kevin Jon Heller, ‘Creating a Special Tribunal for Aggression Against Ukraine Is a Bad Idea’, Opinio Juris, 7 March 2022.

On 17 March 2023, ICC judges issued two arrest warrants against respectively President Putin and Maria Alekseyevna Lvova-Belova, Commissioner for Children’s Rights in the Office of the President of the Russian Federation. According to the ICC, they are ‘is allegedly responsible for the war crime of unlawful deportation of population (children) and that of unlawful transfer of population (children) from occupied areas of Ukraine to the Russian Federation (under articles 8(2)(a)(vii) and 8(2)(b)(viii) of the Rome Statute).’ ‘Situation in Ukraine: ICC judges issue arrest warrants against Vladimir Vladimirovich Putin and Maria Alekseyevna Lvova-Belova’, ICC Press Release, 17 March 2023.

International Court of Justice (ICJ)

On 26 February 2022, Ukraine filed an application instituting proceedings against the Russian Federation before the ICJ. This dispute related to the interpretation, application, and fulfilment of the 1948 Convention on the Prevention and Punishment of the Crime of Genocide (the Genocide Convention). Specifically, Ukraine asked the ICJ to rule that Russia has no legal argument under the Genocide Convention to argue that its military operation against Ukraine is lawful to prevent and punish purported genocide, while claiming that it is in fact Russia who is planning acts of Genocide. Anton Korynevich and Oksana Zolotaryova, ‘Application instituting proceedings on the dispute relating to allegations of genocide (Ukraine v. Russian Federation)’, 26 February 2022, p 8. In parallel, Ukraine requested the ICJ to adopt provisional measures “in order to prevent irreparable prejudice to the rights of Ukraine and its people and to avoid aggravating or extending the dispute between the parties under the Genocide Convention”. Anton Korynevich and Oksana Zolotaryova, ‘Request for the indication of provisional measures’, 26 February 2022, p 7. While not having pronounced on the merits, the ICJ indicated three provisional measures in its Order of 16 March 2022: the Russian Federation has to suspend immediately the military operations that it commenced on 24 February 2022 in the territory of Ukraine; Russia has to ensure that any military or irregular armed units which may be directed or supported by it, as well as any organizations and persons which may be subject to its control or direction, take no steps in furtherance of the military operations; Both Parties have to refrain from any action which might aggravate or extend the dispute before the Court or make it more difficult to resolve. It can be noted that the ICJ in its prima facie assessment considered ‘that Ukraine has a plausible right not to be subjected to military operations by the Russian Federation’. ICJ, Allegations of genocide under the Convention on the Prevention and Punishment of the Crime of Genocide (Ukraine v. Russian Federation), Order of 16 March 2022, p 13 and 17-19; Julian Borger, ‘UN international court of justice orders Russia to halt invasion of Ukraine’, The Guardian, 16 March 2022; Jaime Lopez and Brady Worthington, ‘What’s the Status of Ukraine’s Case Against Russia at the ICJ’, Lawfare blog, 21 April 2022.

European Court of Human Rights (ECtHR)

On 23 June 2022, the European Court of Human Rights (ECtHR) received an application from Ukraine to start a case against Russia, concerning ‘the Ukrainian government allegations of mass and gross human-rights violations committed by the Russian Federation and its military operations on the territory of Ukraine since 24 February 2022.’ On 28 February 2022, the Court received a request for interim measures from Ukraine, following which it requested Russia ‘to refrain from military attacks against civilians and civilian objects, including residential premises, emergency vehicles and other specially protected civilian objects such as schools and hospitals, and to ensure immediately the safety of the medical establishments, personnel and emergency vehicles within the territory under attack or siege by Russian troops.’ Inter-State case Ukraine v. Russia (X): receipt of completed application form and notification to respondent State, Press Release, ECHR 220 (2022), 28 June 2022.

In September 2022, 23 Governments and one non-state actor, the Geneva Academy of International Humanitarian Law and Human Rights, have requested leave to intervene as a third party in the proceedings before the ECtHR. While the Russian Federation ceased to be a party to the ECHR on 16 September 2022, the Court has jurisdiction over the facts that took place before that date, as established by Article 58 of the Convention. Multiple third-party intervention requests in inter-State proceedings Ukraine v. Russia (X), Press Release, ECHR 292 (2022), 23 September 2022.

It should be recalled that currently there are a number of cases ongoing before the Court concerning Ukraine, notably five inter-state cases and several individual applications.

Assistance to Russia

Since February 2022, Belarus has allowed Russia to use its territory to conduct the aggression against Ukraine. ‘Ukraine conflict: UK sanctions Belarus for role in Russian invasion Russia-Ukraine war’, BBC, 1 March 2022. According to the UNGA Definition of aggression, Resolution 3314 (1974), Article 3(f): ‘The action of a State in allowing its territory, which it has placed at the disposal of another State, to be used by that other State for perpetrating an act of aggression against a third State.’ Accordingly, Belarus is committing an act of aggression against Ukraine. However, whether this means that Belarus is party to an IAC against Russia is controversial. On the one hand, the ICRC Commentary to Article 2 common to the Geneva Conventions says that ‘the notion of armed conflict under Article 2(1) requires the hostile resort to armed force involving two or more States.’ ICRC Commentary to Article 2 common to the Geneva Conventions, §218. On the other hand, some authors posit that an act of aggression, even without resort to force, would be sufficient to trigger a NIAC. See e.g. A. Wentker, ‘At War: When Do States Supporting Ukraine or Russia become Parties to the Conflict and What Would that Mean?’, EJIL:Talk!, 14 March 2022. RULAC agrees with the ICRC position that an IAC between two countries is triggered when there is resort to armed froce between them. Accordingly, by allowing Russia to use its territory, Belarus is not a party to the conflict. This position is in lign with the majoritarian approach, whereby there is a strict separation between IHL and jus ad bellum. 

Furthermore, Iran has allegedly provided drones, although Iran has denied these accusations. Allegations also point to the presence of Iranian military trainers in Crimea to help Russian armed forces to operate these drones. ‘Russia, Iran defiant amid UN pressure over Ukraine drones’, Al Jazeera, 20 October 2022; K.Hoper and M. Berg, ‘U.S. confirms Iranian troops in Crimea training Russians on drones’, Politico, 20 October 2022.

On 26 March 2023, President Putin has announced that he intends to station tactical nuclear weapons in Belarus. Notably, in early April a training of Belarus aircrews should start in order to pilot aircraft carrying nuclear bombs, while sotrage facilities for nuclear arsenal should be ready by July 2023. J. Borger, ‘Putin’s timeline for storing tactical nuclear weapons in Belarus is hard to believe’, The Guardian, 26 March 2023.

Assistance to Ukraine

From the outbreak of war between Ukraine and Russia, many states have responded to Ukraine's repeated demands to supply military equipment as well as non-military aid to defend themselves against Russia’s military invasion. In terms of military assistance, in NATO and other countries have supplied Ukraine with defensive lethal weapons and weapon systems, such as anti-aircraft and anti-tank weapons, in the immediate aftermath of the invasion. Moreover, many countries provided Ukraine with helmets, body armour, night goggles, ammunition, fuel, field rations and other military material. This is remarkable given the historical neutrality of supplier states such as Sweden, Norway, Denmark, and Finland. ‘Which countries are sending military aid to Ukraine?’, Al Jazeera, 3 March 2022; Joseph Gedeon, ‘The weapons and military aid the world is giving Ukraine’, Politico, 10 May 2022; Arianna Antezza, André Frank, Pascal Frank, Lukas Franz, Ekaterina Rebinskaya and Christoph Trebesch, ‘The Ukraine Support Tracker: Which countries help Ukraine and how?’, KIEL Working Paper, 18 may 2022, p 21-25;  ‘Arms Transfers to Ukraine’, Forum on the Arms Trade, June 2022.

While these weapons supplies have been mostly defensive in nature, the US announced on 1 June 2022 to provide Ukraine with 4 advanced rocket launcher systems. These M142 HIMARS, have a range more than twice that of the weapon systems they have been equipped with so far, such as the Howitzers supplied by various countries. In addition to the longer range, these weapon systems also bring greater precision. Given this inherent capacity of the M142 HIMARS, the US obtained a formal commitment from President Zelenskyy to only use it for defensive purposes. C. Todd Lopez, ‘Advanced rocket launcher systems heads to Ukraine’, U.S. Department of Defense, 1 June 2022; Joe Gould, ‘US will send HIMARS precision rockets to Ukraine’, Defense News, 1 June 2022.

The supply of weapons and military assistance has raised the question as to whether the countries helping Ukraine should be considered co-belligerents and therefore party to the conflict, inasmuch as they amount to a violation of the law of neutrality. Some authors claim that ‘[o]ne way that a State can become a co-belligerent is through systematic or significant violations of its duties under the law of neutrality.’ C. A. Bradley and J. L. Goldsmith, ‘Congressional Authorization and the War on Terrorism’ (2005) 118(7) Israel Law Review 2048. Hoverver, the majoritarian view seems to disagree and affirms that violating the laws of neutrality doesn’t lead to co-belligerency. Despite this military support to Ukraine, it cannot be concluded that the supplying countries become parties to the IAC between Ukraine and Russia. Indeed, providing military aid as such is insufficient to reach this conclusion. As long as there is no direct military involvement of a state, this state does not become a party to the conflict. M. Schmitt, ‘Providing Arms and Materiel to Ukraine: Neutrality, Co-belligerency, and the Use of Force’, Articles of War, 7 March 2022.

With regard to non-military support, the European Commission is coordinating its largest ever operation under the EU Civil Protection Mechanism. Under this mechanism, all 27 EU countries, plus Norway and Turkey, have offered in-kind assistance ranging from medical supplies and shelter items to vehicles and energy equipment. Other international organisations such as the IMF or the World bank have supported Ukraine financially with respectively an emergency assistance loan of 1.4 billion dollar to Ukraine under the umbrella of the IMF’s Rapid Financing Instrument and a 723 million dollar emergency package. This kind of non-military assistance was also provided for by individual countries. For example, on 4 March 2022, Argentina delivered 1,500 tonnes of food, medicine and clothing, while Australia shipped at least 70,000 tonnes of thermal coal to Ukraine to keep coal-fired generators running, and Israel transported 100 tonnes of humanitarian aid to Ukraine and opened a 66-bed field hospital in Mostyska. ‘Israel sends 100 tons of humanitarian aid to Ukraine’, I24 News, 1 March 2022; Melissa Clarke, ‘Scott Morrison announces visas for Ukrainians, $50 million in military and humanitarian aid’, ABC News, 20 March 2022; Naama Barak, ‘Israel opens humanitarian field hospital in war-torn Ukraine’, Israel 21c, 22 March 2022; Arianna Antezza, André Frank, Pascal Frank, Lukas Franz, Ekaterina Rebinskaya and Christoph Trebesch, ‘The Ukraine Support Tracker: Which countries help Ukraine and how?’, KIEL Working Paper, 18 may 2022, p 13-15; European Civil Protection and Humanitarian Aid Operations, ‘Ukraine: Factsheet’, European Commission, 20 May 2022.

In addition to these forms of support, many countries and international organisations supported Ukraine by taking sanctions towards the Russian Federation. The EU, for instance, has launched 5 packages of sanctions in response to Russia’s military attack against Ukraine and has agreed on a sixth package on 30 May 2022. A First package consisted of targeted restrictive measures targeting inter alia members of the Russian State Duma who recognized the independence of the self-proclaimed Donetsk and Luhansk republics and 27 high profile individuals and entities who have played a role in undermining or threatening the territorial integrity, sovereignty, and independence of Ukraine. These restrictive measures included an asset freeze and a prohibition from making funds available to the listed individuals and entities. In addition, a travel ban applicable to the listed persons prevents these from entering or transiting through EU territory. Moreover, the EU agreed upon an import ban on goods from the non-government controlled areas of the Donetsk and Luhansk oblasts, restrictions on trade and investments related to certain economic sectors, a prohibition to supply tourism services, and an export ban for certain goods and technologies. Finally, the EU imposed financial restrictions by introducing a sectoral prohibition to finance the Russian Federation, its government, and its Central Bank. With every new package, the EU targeted more people, including President Putin and Foreign Minister Sergei Lavrov, and more relevant areas and sectors, such as transport, energy, finance, media, etc. ‘EU adopts package of sanctions in response to Russian recognition of the non-government controlled areas of the Donetsk and Luhansk oblasts of Ukraine and sending of troops into the region’, Council of the EU, 23 February 2022; Gabriela Baczynska and Sabine Siebold, ‘EU imposes sanctions on Putin as Ukraine plead for tougher action’, Reuters, 25 February 2022; Lili Bayer, ‘EU leaders agree ‘maximum impact’ Russia sanctions’, Politico, 25 February 2022; Daniel Boffey, ‘EU to announce sanctions targeting Vladimir Putin and Sergei Lavrov’, The Guardian, 25 February 2022; ‘European Council conclusions on Ukraine, 30 May 2022’, European Council, 30 May 2022; Jan Strupczewski and Philip Blenkinsop, ‘EU, resolving a deadlock, in deal to cut most Russia oil imports’, Reuters, 31 May 2022; Jacopo Barigazzi and Barbara Moens, ‘EU leaders agree on Russian oil embargo’, Politico, 31 May 2022; ‘EU restrictive measures against Russia over Ukraine (since 2014)’, European Council, June 2022.

Furthermore, the G7 leaders agreed on unilateral sanctions, which include inter alia a ban or phase out on Russian oil imports, as well as targeted economic sanctions against Russian economic and financial sectors. ‘Biden says G7 leaders agree on 'devastating packages' of Russia sanctions’, Reuters, 24 February 2022; ‘Russia-Ukraine war: G7 leaders pledge to further isolate Moscow’, Al Jazeera, 8 May 2022; ‘Fact sheet: United States and G7 partners impose severe costs for Putin’s war against Ukraine’, The White House, 8 May 2022; Jeff Mason and Steve Holland, ‘G7 to phase out Russian oil, U.S. sanctions Gazprombank execs over Ukraine war’, Reuters, 9 May 2022. The US, for example, imposed sanctions on Russia's two largest financial institutions immediately after the invasion: Public Joint Stock Company Sberbank of Russia and VTB Bank Public Joint Stock Company. In addition, they imposed sanctions on three additional major Russian financial institutions: Otkritie, Novikom, and Sovcom. A ban was also imposed on the debt and equity prohibitions of major state-owned and private entities. Next to the economic sanctions, they are also targeting sanctions aimed at the Russian elite. ‘U.S. Treasury announces unprecedented & expansive sanctions against Russia, imposing swift and severe economic costs’, The U.S. Department of the treasury, 24 February 2022. Most recently, on 5 February 2023, Europe imposed a ban Sunday on Russian diesel fuel and other refined oil products. D. McHugh, ‘How will EU ban and West’s price cap on Russian diesel work?’, AP News, 5 February 2023.

Other states also imposed sanctions on Russia, mostly in line with the US and European economic actions. Japan and Canada, for instance, matched their sanctions on Russian banks, while Switzerland adopted the EU sanctions towards Russia. ‘The sanctions imposed so far on Russia from the U.S., EU and UK’, Swissinfo, 31 March 2022; ‘What sanctions are being imposed on Russia over Ukraine invasion’, BBC News, 31 May 2022; Minami Funakoshi, Hugh Lawson and Kannaki Deka, ‘Tracking sanctions against Russia’, Reuters, 2 June 2022. The first shipment of the tanks took place on 28 March 2023. ‘Ukraine war: Germany sends much-awaited Leopard tanks’, BBC, 28 March 2023.

On 3 February 2023, Germany announced that it has approved to deliver Leopard 1 main battle tanks to Uraine from its industrial stoks. The announcement was made by Steffen Hebestreit, the government spokesperson. The delivery should take place  as soon as the tanks are repaired, however delais might be possible due to problems in obtaining the required 105-millimetre ammunition. ‘Germany approves Leopard 1 tank deliveries to Ukraine’, The Guardian, 3 February 2023; ‘Germany approves Leopard 1 delivery to Ukraine, in talks with Qatar over Gepards -newspaper’, Reuters, 3 February 2023. On 7 February 2023, Russia’s Defense Minister declared that NATO involvement in the provision of weapons to Ukraine could risk escalating the conflict in unpredictable ways: ‘The US and its allies are trying to prolong the conflict as much as possible. To do this, they have started supplying heavy offensive weapons, openly urging Ukraine to seize our territories. In fact, such steps are dragging NATO countries into the conflict and could lead to an unpredictable level of escalation.’ Moskow has also clarified that the weapons provided by Western countries to Ukraine are legitimate targets. ‘NATO role in Ukraine threatens ‘unpredictable’ escalation: Russia’, Al Jazeera, 7 February 2023. On 19 May 2023, US President Biden announced a new $375 million military aid package for Ukraine. It has been reported that such aid would include ‘artillery shells, armored vehicles and anti-tank weapons.’ Furtermore, the US has authorised third-parties to transfer US F-16 fighter jets to Ukraine and has committed to train Ukrainian pilots. P. McLeary and L. Seligman, ‘Biden set to announce new military aid for Ukraine after meeting with Zelenskyy’, Politico, 19 May 2023.

Both Russia and Ukraine are parties to the four 1949 Geneva Conventions and the 1977 Additional Protocol I. In addition, they are bound by customary international humanitarian law applicable to international armed conflicts. Customary international law consists of unwritten rules that come from a general practice accepted as law. Based on an extensive study, the International Committee of the Red Cross maintains a database on customary international humanitarian law. In addition to international humanitarian law, international human rights law continues to apply during times of armed conflict.

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