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Cooperation among states for the purposes of armed conflict and counterterrorism is increasingly commonplace. In Syria, for example, and in Iraq’s battle with ISIS, various coalitions of states operate behind the scenes, providing each other with a range of support and assistance, often under the radar. Assistance may be operational (embedded soldiers, the supply of weapons, the provision of military bases), but equally may take the form of technical, logistical or financial support. States also increasingly assist one another in counterterrorism situations, for example through the provision of training or intelligence.

The provision of such assistance has legal ramifications. What if, for example, that assistance contributes to a breach of international law? Is the assisting State responsible, as well as the State whose actions broke the law?

This issue is increasingly under the spotlight. Several European states assisting the US in its armed drone programme have been accused of complicity in unlawful conduct. In the UK, two parliamentary select committees have called for the government’s supply of arms to Saudi Arabia for its air strikes against the Iran-backed Houthi rebels in Yemen to be suspended until an independent inquiry into alleged breaches of international law has been completed.

Complicity, and how to avoid it

As cooperation in armed conflict increases, so does the importance of understanding the law on aiding and assisting internationally wrongful acts. International law contains a general rule on aiding and assisting (Article 16 of the Articles on State Responsibility), which provides that a State is internationally responsible for aiding or assisting if it knows of the circumstances of the internationally wrongful act, and if the unlawful act would also be unlawful for the assisting State. There are also specific rules on the subject in certain areas of international law, such as international humanitarian law and international human rights law. Governments need to be aware of these rules and how they apply in practice.

Furthermore, governments should have strategies in place to minimize the risk of facilitating illegal acts. The legal, political and reputational risks of being linked to breaches of international law by other states are significant. This includes the risk of litigation, such as the legal challenge in the High Court regarding the UK’s arms exports to Saudi Arabia.

At the outset, states should have clear policies and procedures for assessing in advance the risks involved before a decision is made on whether to provide assistance. Once this risk assessment has taken place, states have various tools at their disposal to minimize and mitigate risks. These include imposing conditions on assistance (such as a requirement that the recipient state’s actions comply with international law), helping to vet and train recipients of assistance (for example, those operating weapons provided by the assisting state), and obtaining credible assurances from the receiving state (though easier said than done).

States’ assessments of the risks involved also need to be subject to regular review, to reflect the fact that armed conflict and counterterrorism situations are not static, but dynamic and often fast-moving. Weapons provided for an offensive may not trigger responsibility for complicity if the offensive is operated in accordance with the law of armed conflict. But if the recipient State uses those weapons in flagrant breach of the law, the risk assessment changes, and the decision needs to be reassessed.

Publicly available information about states’ strategies for reducing and mitigating the risks of cooperation in armed conflict or counterterrorism situations is limited. The UK’s Overseas Security and Justice Assistance Guidance sets out the procedures for risk assessment that the government should follow when cooperating with other states in security and justice matters (including counterterrorism). Guidance in other sectors and by other governments should also be disclosed. There will of course be some limits to transparency in this area, given the sensitivity of armed conflict and counterterrorism operations, including national security concerns. But basic information about how states understand the legal framework governing their assistance, and the legal norms underlying the acts that they assist, can be made public.

A new Chatham House research paper aims to clarify the law in this area, and makes recommendations to governments for strategies to reduce the risk of assisting in a breach of international law.

But even where there are strategies in place for risk mitigation, monitoring and review, there is of course the issue of political will. In the context of US assistance to Saudi Arabia, the US administration has said that it will ‘review’ its support for the Yemen operation in light of mounting evidence that Saudi Arabia is violating international humanitarian law (for example, in its recent killing of more than 140 people at a funeral). But it remains unclear whether it would go so far as to withdraw support. States that choose to ignore the risks of being held responsible for assistance to unlawful acts act at their peril. As well as being an increased source of litigation, complicity is also receiving increased attention from parliamentary committees, NGOs and international organizations.

The need for states to do their homework before lending a hand – and to keep their assistance under close review - has never been more evident.

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