UK: Letter to Attorney General on US Strikes on Iran from British Bases

Dear Attorney General,

We write to seek urgent clarification on the safeguards the Government has in place to ensure respect for international law in relation to the US military strikes on Iran that are being carried out from UK bases.  

Human Rights Watch is concerned with UK involvement in strikes undertaken by the US from UK bases in the context of the current international armed conflict between Iran, Israel and the US that started on 28 February, as a matter of potential UK involvement in violations of the jus in bello.[1] This is a separate question from the jus ad bellum lawfulness of the UK’s involvement in the conflict (which is beyond Human Rights Watch’s mandate).

On 1 March 2026, the Prime Minister confirmed that the United Kingdom had agreed to a US request to use British military bases, for what he described as the "specific and limited defensive purpose" of "tak[ing] out Iran’s capability to launch these attacks, which of course means taking out the launchers and the infrastructure that sits behind them." The legal summary published by the government invoked collective self-defence of Gulf allies and the protection of British lives and nationals as the legal basis for that decision and does not mention jus in bello issues. The jus ad bellum justification is not the concern of this letter.

When the Foreign Secretary was asked on 2 March whether the Government would approve targets and monitor the outcome of each US strike from a UK base, whether it would report to the Intelligence and Security Committee, and whether it would suspend base access if a strike hit something other than a missile battery or store, the Foreign Secretary responded that "longstanding operational arrangements for partners and allies" would be implemented.

In the current context, international humanitarian law (IHL), international criminal law (ICL) and general international law including the rules on state responsibility as relevant to IHL and ICL, are applicable to the UK’s decision to allow the US to use its military bases to strike targets in Iran. With respect to IHL, Common Article 1 of the Geneva Conventions (hereinafter CA1) places a duty on states to ensure respect for international humanitarian law. This obligation[2] has an external dimension that requires states to do everything that is reasonably in their power to ensure respect by others that are Party to a conflict.[3] While the UK government has reiterated its longstanding position more recently in the Al Haq case[4] that CA1 does not have an external component, this is inconsistent with well documented practice[5] and such a blanket approach as outlined by the government fails to take account of: how the obligation may arise in the context of joint military operations or where a state is providing support (and in this instance concrete and meaningful support that is directly linked to a possible risk of a violation of IHL) to another state in the context of military operations, where the issue of ability to influence is clear (and in this instance has already been made out, given that the UK has already conditioned the use of the base in terms of targets) and that the external dimension of CA1 it an obligation of conduct not result.

While it is certainly the case that the contours of the external obligation under CA1 differ depending on the circumstances, the duty is particularly pronounced when states are providing support to a party to the conflict (either as a co-party to the conflict or as a third party providing support to a party to the conflict).[6] The duty comprises both a negative and positive obligation. The negative obligation is that a state may neither encourage nor aid and assist in violations of the Conventions.[7] Providing support, which would include the use of a military base, with the knowledge that such support will contribute to violations of IHL would violate CA1.

Relatedly, the positive obligation under CA1, means that states must take proactive steps to bring violations of the Conventions to an end by exerting influence on that party.[8] Importantly, this obligation is not limited to stopping ongoing violations; it also includes an obligation to prevent violations when there is a foreseeable risk that they will occur and to prevent further violations in case they have already occurred.[9] Given that the obligation is one of conduct not result and imports a standard of due diligence, the question of whether a duty has been carried out will depend on the specific circumstances, including the means reasonably available to the state and the degree of influence it exercises over those responsible for the breach. As the International Committee of the Red Cross 2016 Commentary on the First Geneva Convention of 1949 provides, “the duty to ensure respect for the Geneva Conventions is particularly strong in the case of a partner in a joint operation, even more so as this case is closely related to the negative duty neither to encourage nor to aid and assist in violations of the Conventions. The fact, for example, that a High Contracting Party participates in the financing, equipping, arming or training of the armed forces of a Party to a conflict, even plans, carries out and debriefs operations jointly with such forces, places it in a unique position to influence the behaviour of those forces, and thus to ensure respect for the Conventions.”[10] While UK support in this context does not necessarily qualify as a joint operation, the strength of the positive duty is derived from the degree of practical cooperation provided and the feasibility of taking action in the circumstance. What is feasible will depend, inter alia, on the degree of coordination and the ability to influence the conduct of parties.

In this context, the United States has requested the use of UK bases to carry out certain strikes on Iran (which presumably it would otherwise be unable to do or would find difficult), and the UK has explicitly authorised the use and reportedly limited and defined the scope of any such use. In accepting the US request, the UK is providing support to a party to the conflict and in providing permission and reportedly limiting the scope of its acceptance, it is demonstrating it is in an unique position to influence US conduct in respect of the strikes carried out from UK bases. It follows that in these circumstances, the UK has a particularly heightened duty to ensure respect for IHL including the obligation to take precautions to protect civilians. Should a foreseeable risk of breach of IHL by the US arise in this context, or a violation occur, the UK is required to utilize its apparent power and influence to ensure respect for IHL by taking concrete steps to influence the US to comply with its obligations including investigations into any suspected violations committed in or from UK territory.

Additionally, under Article 16 of the Articles on State Responsibility, a state that knowingly provides aid or assistance in the commission of an internationally wrongful act bears independent legal responsibility for that act. Given that the United Kingdom has authorised the US to use its bases for certain operations, if an internationally wrongful act were to result from these operations, it could engage the UK’s liability under Article 16.

The prospect that the UK is assisting the US with the use of explosive weapons in populated areas raises additional concerns under the 2022 Political Declaration on Strengthening the Protection of Civilians from the Humanitarian Consequences Arising from the Use of Explosive Weapons in Populated Areas. As an endorsing state, the UK has politically committed to “actively promote this Declaration” and to “pursue its … effective implementation” by other states. The UK should thus encourage the US, also an endorsing state, to implement the Declaration’s commitment to restrict and refrain from the use of explosive weapons in populated areas rather than facilitate the use of those weapons.

Since the start of the second Trump administration, the Defense Department under Secretary Hegseth has deliberately and systematically weakened the protections meant to ensure compliance with the laws of armed conflict. This includes, removing senior military lawyers without publicly citing misconduct, and replacing the Army, Navy, and Air Force judge advocates general, directly undermining legal oversight of combat operations. It has also abolished “civilian environment teams” and other mechanisms specifically designed to limit harm to civilians during operations.[11] Finally, the 2026 National Defense Strategy omits references to civilian protection and international law entirely. These changes are especially concerning in light of Defense Secretary Pete Hegseth’s comments dismissing what he calls "stupid rules of engagement," suggesting they interfere with "fighting to win." In response to concerns about the conduct of the US government, it is reported that late last year your Government paused some intelligence-sharing with the US on suspected drug trafficking vessels in the Caribbean amid concerns information supplied may be used to engage in unlawful military strikes by American forces.

In addition to this, there are already concerns about US compliance with IHL in the context of apparent US strikes on civilian infrastructure in Iran. On February 28, an unlawful attack was carried out on Tayyebeh primary school in Minab in southern Iran that reportedly killed 168 civilians, including schoolchildren. It has been reported that a preliminary inquiry by the Pentagon has found that the US was responsible for the attack and that it occurred due to outdated US targeting data. As far as we understand it, this strike did not involve the use of a UK military base, but this incident raises questions about the US approach to civilian harm and in particular, the systems in place in the US Department of Defence to limit civilian harm and ensure compliance with the principles of distinction, proportionality and necessity, as well as to take all feasible precautions to protect civilians. It also raises questions about the role that any artificial intelligence or automated systems play in determining targets.

In circumstances where the UK clearly has a degree of influence over the US in relation to the strikes that are conducted from its bases, and where there are very real reasons to be concerned about the extent to which the US has the institutional safeguards in place for civilian protection and a commitment to comply with IHL, the UK should be taking proactive steps, beyond limiting the permissible targets, to ensure that the US respects IHL when it is using its bases to strike Iran. Relatedly, the UK should have safeguards in place to ensure that it does not aid and assist any violations of international law (both in relation to the negative obligation of the duty to prevent under CA1 and the obligations not to aid and assist in an internationally wrongful act under Article 16 of the ASR).

Senior UK military and government officials are also subject to international criminal law. In addition to liability under certain circumstances arising out of aiding the commission of serious international crimes, including through providing the means for their commission, military and civilian commanders or superiors may be individually criminally responsible for international crimes committed by forces under their effective command and control, or effective authority and control, when they fail to take all necessary and reasonable measures to prevent such crimes they knew or should have known about, or fail to submit the matter to the competent authorities for investigation and prosecution. [12] We note that the UK has failed to fully incorporate and extend into all overseas territories its treaty obligations under relevant law, in particular by not extending the application of the International Criminal Court Act to the British Indian Ocean Territory (BIOT), including the Diego Garcia base.

In light of the abovementioned facts, which appear to give rise to a degree of foreseeable risk of possible violations involving unlawful civilian harm by the United States in strikes on Iran (even those limited to targets authorised by the UK), we ask the Government to respond to the following questions:

1. What steps has the UK government taken to ensure that the United States is respecting IHL when carrying out strikes from British bases beyond reportedly limiting the targets of those strikes? To the extent possible, please outline what specific steps have been taken to ensure that US military strikes on Iran from UK bases are compliant with IHL?
2. Relatedly, what institutional safeguards are currently in place to ensure that the UK government is not facilitating a breach of IHL in the context of US strikes on Iran from UK bases?
3. Is the UK relying on the ‘longstanding arrangements’ which the Foreign Secretary referred to on 02 March to ensure compliance with its international obligations and if so, what steps have been taken to ensure they are adequate for the purpose of the UK complying with its international obligations given the abovementioned facts?
4. Is the UK involved in selection and verification of targets and the precautions taken to spare civilians? Or is there any prior mandatory review of targets by the UK Government?

5. Does the UK Government monitor the outcomes of individual strikes, and if strikes were to cause civilian casualties or damage to civilian objects, what steps would it take?

6. What conduct by the US military would cause the UK to cease its facilitation of any specific or all operations from its bases?

7. What requests has the UK Government made to the United States to understand US assessments of responsibility in connection with the February 28 attack on a compound in Minab County, Hormozgan province in Iran that struck several buildings including a primary school - a protected civilian building; the reasons for that strike; the intended military target, and any precautions taken to minimize the civilian harm?

8. What steps has the UK government taken to fulfill its commitment under the Political Declaration on Explosive Weapons in Populated Areas to promote implementation of the Declaration with the US?

9. What steps has the UK government taken to ensure that bases on UK territory, and senior UK civilian and military officials are not implicated in any form of assistance to possible war crimes by US or other forces operating from these bases? Will the UK government ensure that any allegation of war crimes being launched or planned from UK territory, or with the assistance of UK nationals, is promptly investigated with prosecutions of anyone responsible for crimes under international law?

10. Is the UK providing any other forms of aid and assistance (including intelligence), or otherwise cooperating with the US or Israel in the context of the international armed conflict with Iran and if so, please outline what this cooperation and assistance is, and what steps have been taken, and safeguards are in place, to ensure the UK is complying with its international obligations in the provision of that assistance or cooperation.

11. Will the UK government clearly state that its own obligations under IHL and ICL apply to all its territories where there are military bases, including BIOT and the Sovereign Base Areas, and extend all relevant laws to these territories, including the International Criminal Court Act?

While we appreciate that the government has published a summary of its legal position on the legality of its defensive action in respect of Iranian regional attacks, this did not set out how and in what ways the government was acting in accordance with international humanitarian law, international criminal law and the law on state responsibility when allowing the US to use UK military bases to launch strikes against Iran. These are questions that it is important for the government to answer, particularly given the significant risk of civilian harm and the risk of UK involvement in that harm.

We would be grateful for the Government's substantive response to each of the above questions.

Sincerely,

Yasmine Ahmed.