Supplying Arms to Parties to a Conflict: When is it Legal?

The table above represents primary rules of international law for which State responsibility may be incurred. While Article 16 of the ILC Articles on the Responsibility of States for Internationally Wrongful Acts [‘ARSIWA’] is included with other secondary rules, it is in fact a primary rule.

For any State to allege State responsibility on the part of a third State in supplying arms or funding to a belligerent State/responsible State in a war, they would first have to establish that the conduct, by act, omission, aid or assistance, is unlawful and that the unlawful act is attributable to the responsible State. The legal obligations broadly surrounding the arms trade also exist in different sources of law. For instance, traditionally, the law of neutrality has prohibited States from providing military equipment or intelligence to belligerent States. This was primarily so that such States were not to be attacked and their territory was to remain inviolable. However, as a result of the incorporation of the prohibition on the use of force under Article 2(4) into the United Nations Charter, some argue that the law of neutrality is no longer relevant.

Moreover, various jus cogens norms create positive or negative obligations erga omnes such as prohibition of genocide, crimes against humanity, prohibition of slavery, aggression, torture and more that would also activate a third State’s duty to prevent supply of arms to a State or non-state actor who is at a ‘likely or foreseeable’ (Nicaragua v. United States of America), Merits, Judgment, I.C.J. Reports 1986, para. 256) risk of committing these unlawful acts and the supply of arms is likely to contribute to the breach. Additionally, primary rules also exist in the Genocide Convention (1948), the Geneva Conventions (1949), the Arms Trade Treaty (2014), as well as any Security Council Resolution which place an arms embargo on parties to the conflict.

State responsibility is engaged by virtue of the ILC Articles [‘ARSIWA’]. Article 2 states that an act or omission of a State constitutes an internationally wrongful act if it breaches an international obligation. Article 16 outlines various forms of wrongful assistance, including aiding and assisting. Article 40 surrounds the serious breach by a State of an obligation arising under a peremptory norm, and Article 41 calls upon States to ‘cooperate to bring to an end through lawful means any serious breach within Article 40’. This can also apply in the concept of supplying arms to a State that is committing a breach of international law and cooperating in a way to end the breach by suspending or halting the supply of arms or military equipment to the belligerent State.

2.1 Case Study: The Russia and Ukraine War

2.1.1 The Legality of Supplying Arms to Ukraine

The Russian-Ukraine war provides an interesting case study in the context of State-State arms transfers. Western States have supported Ukraine in various forms, from humanitarian aid to military assistance. In May 2022, the European Union [‘EU’] allocated €1.84 billion for supplying military equipment to Ukraine’s armed forces. Traditionally, in an international armed conflict, the principle of neutrality (as mentioned above) would apply, requiring States to maintain a neutral stance aimed at containing the conflict and discouraging broader involvement worldwide. Some have argued that an exception to neutrality is triggered when one State is a clear aggressor and another a victim. The UN General Assembly [‘UNGA’] declared Russia’s invasion of Ukraine to be an act of aggression in a 2022 resolution. A similar vote at the Security Council was not possible due to Russia’s veto as a member of the Permanent Five

In cases where the belligerent and injured States are clearly identifiable, some scholars argue that supplying arms can be seen as fulfilling the positive duty under Article 41 ARSIWA to bring an end to a serious breach under Article 40. While States are not necessarily obliged to supply arms to meet this positive duty, the wording of Article 41 and the UNGA resolution leaves it open for States to employ measures they deem appropriate in support of Ukraine. There is therefore a view that supplying arms by third States to Ukraine is lawful under international law as it is a victim of aggression.

This can also be supported in part by the reference to collective self-defence in Article 51 of the UN Charter. As Ukraine is the victim of an armed attack, it has the right to request assistance in the form of collective self-defence from its allies. Arguably, if this extends to the right to use force against the aggressor State, it would also extend to providing arms and assistance to the State which is the victim of aggression. A key difficulty in this approach, however, is the lack of reporting of self-defence measures by assisting States to the Security Council under Article 51 as well as the question of whether the parties supplying Ukraine under Article 51 would become co-belligerents to the conflict.

It seems though that only supplying arms without more (i.e. engaging in acts that have a “sufficiently direct connection to harm to the adversary”) would not result in co-belligerent status. However, Wentker argues that the US’ provision of intelligence to Ukraine “may form part of concrete military operations, such as targeting processes”. While details on this assistance is vague, he acknowledges that “if such operations were to be integrated into and closely coordinated with Ukraine’s military operations, they could bear out a sufficiently close connection to harm caused to the adversary to make the State providing them a party”.

In conclusion, as Ukraine is the clear victim of an act of aggression, it is arguable that this creates an exception to the law of neutrality in allowing the transfer of arms to the victim State. This is supported by the fact that the supply of arms arguably is in furtherance of the duty to bring an end to a serious breach of a peremptory norm under Article 41 ARSIWA and is supported by the fact that a State may request assistance in collective self-defence when victim of an armed attack under Article 51, UN Charter. Whether these assisting States subsequently become ‘parties to the conflict’ too depends on the extent of the support they provide and whether this causes sufficiently direct harm to the adversary.

The lawfulness of the support however would end if Ukraine used those arms to commit genocide, crimes against humanity, war crimes, or human rights violations as per State’s obligations under Articles I and III of the Genocide Convention (1948), Common Article I of the Geneva Conventions (1949), Article 16 of ARSIWA and, for those States party, Article 6(3) of the Arms Trade Treaty (2014). This is particularly relevant in the case of Israel which, if the argument that it was the victim of an armed attack on October 7, 2023 and can act in self-defence in occupied territory is accepted, would run afoul of any exception in the law of neutrality by virtue of the fact that it is plausibly committing a genocide in the Gaza Strip (explored further in Section 2.2 below).

2.1.2. The Illegality of Supplying Arms to Russia

In contrast, Russia is the aggressor in this war, given there does not seem to be a case in favour of self-defence against an armed attack by Ukraine under which Russia’s use of force would be lawful. Therefore, States supplying weapons to Russia, such as Iran, North Korea, and China, are likely violating the law of neutrality and Article 16 ARSIWA by providing aid and assistance to Russia if those weapons are used or contribute to Russia’s internationally wrongful acts.

China has denied supplying any arms to Russia despite Ukraine alleging that ‘as of early 2025, 80 per cent of critical electronic components found in Russian drones originated in China’. In 2024, G7 countries stated that the transfer of weapons components from China was enabling Russia to ’reconstitute and revitalise’ its defence production for its war in Ukraine. As it is a war of aggression which is ongoing and therefore a continuing internationally wrongful act, if proven, this statement indicates that China would be responsible under Article 16 and Article 41 ARSIWA as well as Common Article I of the Geneva Conventions (1949) given evidence of Russian war crimes. This is particularly so in light of the ICJ preliminary order that Russia was to “immediately suspend the military operations that it commenced on 24 February 2022 in the territory of Ukraine” (Ukraine v. Russia, Preliminary Order of March 16, 2022, para.81)

Additionally, Iran has supplied Russia with munitions, artillery shells, and drones and therefore would run afoul of the same laws as China. North Korea has also reportedly supplied millions of munitions, rockets and artillery which would also engage the laws mentioned above, as well as North Korea specific Security Council Resolutions such as Resolution 1894 [2009]. Moreover, North Korea has gone further than China or Iran in providing troops which have been deployed on the battlefield. In doing so, it has arguably gone from being an accomplice to a principal in the commission of the act of aggression against Ukraine.

Any aid provided which significantly, substantially, or materially contributes to Russia’s commission of aggression against Ukraine either with the purpose of doing so, indirect intent to do so or wilful blindness, constitutes a violation of international law. Therefore, China, Iran and North Korea, may have violated Articles 16 and 41 of ARSIWA, Common Article I of the Geneva Conventions as well as the law of neutrality. North Korea may have also violated Article 2(4) of the UN Charter in committing a direct act of aggression against Ukraine in deploying troops. And China, as the only State party, may also have violated Article 6(3) of the Arms Trade Treaty.

2.2 Case Study: Supplying Arms to Israel

The Genocide Convention binds each State party to the Convention to prevent and to punish genocide (Article I), and acts of conspiracy to commit genocide and complicity in genocide are also punishable (Article III). Valentina Coli defines complicity as a form of “knowing involvement of an international law actor in the wrongful act that can be attributed to another.” In Bosnia’s genocide case against Serbia at the ICJ [2007], the ICJ held that the duty to prevent genocide is ‘one of conduct and not of result’ and ‘State parties are to employ all means reasonably available to them, so as to prevent genocide’, the duty on each State to discharge this burden is subject and operates under various parameters such as the State’s geographical distance, capacity to influence action, political relations and more (para.430). The duty to prevent genocide is extensive. It imposes responsibility on all States in any of their dealings with a génocidaire State. This duty can extend to the supply of weapons, whereby third States supplying arms are aware of a serious risk that a genocide is ongoing and yet continue to supply weapons, often with caveats, in a manner that enhances the military capabilities of the génocidaire State, plausibly breaching the duty to prevent genocide.

2.2.1 Cases Concerning Israel’s Occupation at International Forums

In South Africa’s genocide case against Israel at the ICJ, the court granted provisional measures to South Africa on three different occasions in January, March and May 2024.. It recognised that “at least some of the rights claimed by South Africa and for which it is seeking protection are plausible. This is the case with respect to the right of the Palestinians in Gaza to be protected from acts of genocide and related prohibited acts identified in Article III” (Order of 26 January 2024, para 54) and that the rights are of ‘such a nature that prejudice to them is capable of causing irreparable harm’ (para 66), and that “.This ruling further raised a risk for States supplying arms to Israel of their potential breach of international law obligations, with Israel in this context being the potential génocidaire State against Palestinians.

In 2024, Nicaragua filed a case against Germany at the ICJ, mainly asserting that by supplying weapons to Israel, Germany has failed to meet its obligations under the Genocide Convention, the Geneva Conventions and their Additional Protocols, and denied Palestinians the right to self-determination. This is a case concerning one State’s responsibility in supplying arms to another State. Nicaragua requested provisional measures from the court; the court refused them; however, the case remains on the court’s General List. This case will be important in delineating the rules relating to arms transfers in international law and the framework which applies to States supplying arms to a party to the conflict which the ICJ has ruled is ‘plausibly’ committing a genocide.

In July 2024, ICJ handed down a further advisory opinion the Legal Consequences arising from the Policies and Practices of Israel in the Occupied Palestinian Territory [‘OPT’] and called on all States not to ’render aid or assistance in maintaining the situation created by Israel’s illegal presence in the OPT’ and all the States parties to the Fourth Geneva Convention ‘to ensure compliance by Israel with international humanitarian law as embodied in that Convention’ (para 279). In August 2025, the UN’s Independent International Commission of Inquiry on the Occupied Palestinian Territory found that Israeli forces have committed genocide and urged all Member States to ‘cease aiding or assisting… by reviewing all relationships with Israel, such as… arms transfers’ [90(c)].

Third States have a wider obligation to respect international humanitarian law as well. In its 2004 Advisory Opinion addressing the construction of a wall, the ICJ issued a definitive interpretation of the relevant international humanitarian law (IHL) obligation: ‘States that are parties to the Geneva Convention concerning the protection of civilian persons in times of war, adopted on August 12, 1949, are legally required…..to ensure that Israel complies with the international humanitarian law as outlined in that Convention’ (para 159).

In October 2025, the Special Rapporteur published a report titled ‘Gaza Genocide: a collective crime’ focusing, amongst other forms of complicity, on how the ‘Large-scale military aid, cooperation and arms transfers, primarily to and from the United States of America and European States, have enabled Israeli domination over the Palestinian people’. The Special Rapporteur rejected the argument used by States to justify the supply of arms to Israel to be used for ‘defensive’ purposes and noted that ‘Given that the occupation of Palestinian territory is an ongoing unlawful use of force in violation of the Charter of the United Nations, nothing Israel does there can be understood as defensive’ (para 41). As noted above, in relation to the exception provided to Ukraine in allowing for arms transfers to States which have been the victim of aggression, this exception would end where that State commits internationally wrongful acts with those weapons.

In this case, further provision of arms to Israel would run afoul of a number of these laws, notably the Genocide Convention (1948), particularly in light of the ICJ’s preliminary order in South Africa v. Israel (Order of 26 January 2024), Common Article I of the Geneva Conventions (1949), and Article 16 and Article 41 ARSIWA, particularly in light of the ICJ’s Advisory Opinions of 2004 and 2024. These laws would apply even were Israel to be acting in self-defence under Article 51 of the UN Charter against an armed attack by Hamas, a claim which is itself not without difficulty.

2.2.2. Cases at Domestic Forums

There have been some notable cases around the world in domestic contexts concerning the Israel–Hamas conflict, centered on the export of arms to Israel. Last year, two NGOS in the UK, Al-Haq and Oxford, brought judicial review proceedings against the Secretary of State for Business and Trade for continuing to supply F-35 components to Israel and for failing to suspend the supply and export licenses entirely. The High Court handed down a 72-page judgment and rejected all of the claimants’ grounds. The court deferred the decision to the executive, which the court said is ‘democratically accountable to Parliament and to the electorate,’ and ruled that it is within their jurisdiction and discretion. In its conclusion, the court noted that this case ‘has not been about whether the UK should supply arms or other military equipment to Israel; that decision has been made by the Secretary of State,’ but rather whether ‘it is open to the court to rule that the UK must withdraw from specific multilateral defence collaborations which are reasonably regarded by the responsible Ministers as vital to the defence of the UK and to international peace’ [para 206, 207].

The Dutch brought a similar case and the Appeals court ruled against the government and stopped the transfer of parts of F-35 fighter jets to Israel. This was overturned in October 2025 by the Dutch Supreme Court who ordered the executive to reassess the export licence of F-35 components (AV009) to Israel (section 7 of the judgment). In India, a public interest litigation was filed with the Supreme Court in September 2024 to cancel existing licences and permissions and to stop issuing new licences to companies in India for exporting arms and military equipment to Israel amid the ongoing Gaza conflict [para 2]. The petition was dismissed because the court held that the issue of arms exports falls within the domain of foreign policy.

Amnesty Denmark, together with three other NGOs, filed a case against the Danish government regarding the supply of F-35 fighter jets to Israel. That case is still awaiting a final decision. Some countries that have suspended or halted arms trade to Israel include Belgium, Italy, Spain, the Netherlands, Canada and Japan and Slovenia. In November 2024 the Coalition for Canadian Accountability in Gaza (CCAG) with the Legal Centre for Palestine filed a case against the Canadian government for ‘failing in its duty to take all reasonable measures to prevent genocide, including by continuing to militarily cooperate with Israel and permitting record exports of arms and other military equipment’. That case is also still ongoing.

Most cases have resulted in similar outcomes, showing deference to the executive. The various organisations approached their respective courts due to a lack of confidence in the executive’s willingness to take a firm stance against the supply of arms; they expected decisions based on each State’s domestic and international legal obligations to be reviewed by the appropriate authority, the courts. Despite national court rulings, the UN’s findings and evidence submitted to the ICJ reveal multiple violations of international law by Israel, including a plausible risk that genocide may have taken place or is ongoing.

International law does not demand absolute certainty from States that their actions, such as arms supplies, support unlawful acts; probable support is enough, and this has already been established in this case. In Bosnia v Serbia [2007] the ICJ clarified that ‘it is irrelevant whether the State whose responsibility is in issue claims…. that even if it had employed all means reasonably at its disposal, they would not have sufficed to prevent the commission of genocide. This is irrelevant to the breach of the obligation of conduct in question…. since the possibility remains that the combined efforts of several States, each complying with its obligation to prevent, might have achieved the result’. [para 430]. The judgment very crucially reemphasises the power of communal action of the international community; it shows that every action matters as long as the effort to prevent genocide (or arguably any other internationally wrongful act) is clear. Given that many governments remain hesitant to stop arms and component exports to Israel, this raises a grave concern about whether ‘all means reasonably at a [State’s] disposal’ have been used to prevent genocide.

1. State to Non-State Actors Arms Transfers

The table below summarises the instances in which a State may not transfer weapons to a non-state actor and potential exceptions to these rules: