When Restraint Becomes Complicity

The US-Israeli attacks against Iran, launched on 28 February 2026, have plunged the Middle East into a dangerous and expanding conflict – triggering a broader factual and normative wildfire. What is significant about this conflict is not simply its rapid escalation, but the open defiance of fundamental rules of international law, which also raises serious questions regarding the responses of third states to the US-Israeli attacks. Concretely, facilitating acts of the US-Israeli attacks against Iran could amount to complicity under Art. 16 of ARSIWA and constitute a violation of the law of neutrality. Conversely, facilitating unlawful and disproportionate Iranian retaliatory strikes falling outside of the scope of self-defence could equally engage the international responsibility of third states.

The Legal Baseline of the US-Israeli attacks and Iran’s response

It is widely acknowledged that the US-Israeli attacks violate the prohibition on the use of force under Art. 2 (4) of the UN-Charter and qualify as an act of aggression. The US justification attempts relating to self-defence under Art. 51 of the UN-Charter – whether as “pre-emptive self-defence” against an Iranian nuclear attack that was not even near imminent, or as “double pre-emption self-defence” to forestall potential attacks on US bases, should Israel have acted alone, are legally untenable and not supported by any facts. Equally, a justification based on humanitarian intervention and anticipated regime change lacks any recognised legal basis – far from being able to be factually achieved by the current conduct of the US.

The alternative US claim, stated in its letter to the UN Security Council, that the operations form part of “an ongoing international armed conflict” referenced in connection with Operation Midnight Hammer in June 2025 is equally unconvincing. The administration cannot simultaneously invoke self-defence and an ongoing armed conflict as legal bases for its attacks. Even if an IAC does not end with the mere cessation of active hostilities, the absence of Iranian attacks against the US after the twelve-day war in June 2025 and active diplomatic negotiations on its nuclear programme in the weeks before 28 February 2026 mean that the temporal dimension of military necessity for the current attacks is not even satisfied under the jus in bello. Far from being a war of necessity, the war against Iran is a war of choice and if Trump is taken at his word, it is also a war for fun.

In response to these unlawful attacks, Iran is entitled to take necessary and proportionate measures of self-defence under Art. 51 of the UN-Charter. Such acts, however, must remain within the framework of IHL and cannot extend to retaliatory strikes against civilians or objects in third states. Iran’s strikes on civilian infrastructure in Gulf states manifestly exceed the scope of lawful self-defence and are themselves violations of international law. Similarly, the closure of the Strait of Hormuz violates the right of transit passage under Art. 37 of ff. UNCLOS, unless the closure is applied exclusively in Iranian territorial waters to the vessels of belligerent states or unless Oman, which borders the opposite side of the Strait of Hormuz, has become a belligerent through Iranian strikes on its territory, such that the entire Strait of Hormuz would be encompassed by the territorial waters of belligerent states.

Third State Responses: From Restraint to Complicity

For third states committed to international law, this legal baseline has important implications for their engagement with this conflict. Open alignment with the US-Israeli war against Iran carries legal and strategic risks – from complicity to entanglement in a widening conflict that has already destabilised the Middle East.

Besides direct involvement as a co-belligerent in the armed conflict, two legal regimes are central to assessing the conduct of third states in relation to the US-Israeli attacks: the law of state responsibility and the law of neutrality.

Complicity under ARSIWA

Under Art. 16 of ARSIWA, a state incurs international responsibility when it aids or assists another state in committing an internationally wrongful act, provided it has knowledge of the circumstances. Additionally, the act must be internationally wrongful if committed by the assisting state. This is also called complicity in the international wrongful act of another state. Crucially, Art. 16 of ARSIWA requires a wrongful primary act. Assisting lawful conduct – such as self-defence acts under Art. 51 of the UN-Charter – does not trigger Art. 16 of ARSIWA. Accordingly, supporting the US or Israel in their international wrongful attacks against Iran amounts to complicity (the knowledge of the international wrongfulness of their acts put forward) – vice versa, while assisting Iran in unlawful retaliatory strikes against uninvolved third states or civilian objects equally engages responsibility – depending on the knowledge of the assisting state. Conversely, support for Iranian strikes against legitimate military objectives in self-defence would not fall under Art. 16.

A second avenue arises from Art. 41 of ARSIWA and, as some scholars argue, reinforced by the 2024 ICJ Advisory Opinions on Palestine. The Court clarified that all states are under an obligation not to recognise as lawful a situation created by serious breaches of obligations erga omnes or, under Art. 41 of ARSIWA, of peremptory norms of international law. Furthermore, the states are obliged not to render aid or assistance in maintaining that situation, and to refrain from entering into economic or trade dealing with Israel concerning the Occupied Palestinian Territory which may entrench Israel’s unlawful presence there.

The Law of Neutrality

The traditional view on the law of neutrality, most comprehensively codified in the Hague-V- and Hague-XIII-Convention as well largely reflected in customary international law, sets out the rights and duties of neutral states to refrain from any support of a belligerent (on an impartial basis) and, conversely, to remain unaffected by the international armed conflict – particularly, the duty of belligerents not to use neutral territory as a base of military operations (Art. 5, 8 of Hague XIII), not to erect military communications infrastructure on neutral territory (Art. 3 lit. a of Hague V) or to use such infrastructure, established prior to the outbreak of the international armed conflict, for military purposes (Art. 3 lit b of Hague V).
A neutral state that fails to prevent a belligerent from undertaking such acts on its territory is itself in breach of its duties of neutrality, and the opposing belligerent may adopt proportionate countermeasures in response to terminate the violation of neutrality. The decisive distinction from Art. 16 of ARSIWA is that the law of neutrality prohibits support to either belligerent irrespective of whether an internationally wrongful act is thereby assisted.
While the normative status of this framework since the Russia-Ukraine-war has come under increasing pressure, reviving the concept of “qualified neutrality” and leading some scholars to call for the death of the law of neutrality, it still remains part of customary international law and continues to provide a clear framework for the conduct of third states, particularly where all partied involved claim that their conduct does not violate international law.

UK

Permitting the use of British bases for US strikes raises serious legal concerns under the above-stated frameworks. Facilitating the actions of an unlawful aggressor can amount to complicity under Art. 16 of ARSIWA and may itself constitute an act of aggression under Art. 3 (f) of the Annex to the UNGA-Resolution 3314. It would also violate neutrality law, specifically the prohibitions against using neutral territory as a base of military operations (Art. 5, 8 of Hague XIII) or for the transit of belligerent forces (Art. 2, 11 of Hague V).

The restrictions reportedly imposed by the UK on the US use of its bases – limiting it to “defensive action against missile facilities in Iran which were involved in launching strikes at regional allies” – might suggest, in theory, a different legal assessment, but under the current circumstances there is no room for a different legal assessment. Where all US-Israeli attacks form part of the war of aggression, no individual strike can credibly be isolated as purely defensive when it is facilitated by the same infrastructure and equipment.

Germany

Germany faces analogous concerns, especially when looking at Ramstein Air Base, which is reportedly being used at least as a logistical hub for operations against Iran. Should operations against Iran be directly launched from these bases, the legal assessment could mirror that previously discussed with respect to the UK.

A further dimension concerns Ramstein’s potential role in drone operations. In earlier proceedings on US drone strikes in Yemen, neither the Federal Administrative Court of Germany nor the Federal Constitutional Court of Germany identified a violation of international law arising from the relay of data used for drone control. In the context of the war against Iran, however, the legal assessment is likely different. If Ramstein were used to relay data enabling the control of drones conducting strikes in Iran, there would be indications giving rise to a serious risk of systematic violations of international law, given that such strikes would form part of a war of aggression violating the prohibition on the use of force.

Permitting such use would engage Germany’s responsibility on multiple levels: complicity under Art. 16 of ARSIWA and – most directly – the law of neutrality. Art. 3 of Hague V, prohibits the use of pre-existing military installations for communication with armed forces in the field. The relay of data from Ramstein enabling the control of drones conducting strikes in Iran would fall within this prohibition.

India and the Strait of Hormuz

India secured diplomatic exemptions for Indian vessels to transit Iranian-controlled waters. This behaviour of negotiating exemptions for Indian vessels warrants a closer look at complicity according to Art. 16 of ARSIWA, as the closure of the Strait of Hormuz could be viewed as an international wrongful act (see above) and negotiating exemptions from it might be seen as supporting Iran in maintaining it. However, to negotiate the non-application of a wrongful act to one’s own assets is to seek restoration of the legal order for that state. Treating such conduct as complicity would prevent states from protecting their own nationals and interests against wrongful acts – an untenable result.

A more nuanced answer can be drawn by analogy to the 2024 ICJ Advisory Opinions on Palestine, which articulated a duty for states not to recognize and support unlawful situations created by a wrongfully acting state – including a duty to refrain from entering into dealings that may entrench such unlawful situations. India’s bilateral negotiations of passage rights could, on this reasoning, risk normalising an unlawful closure of the Strait, in a manner broadly analogous to the duty not to deal with Israel on terms that recognise its unlawful presence in the OPT. However, that analogy has serious limits. The 2024 ICJ Advisory Opinion on Palestine was developed in the context of a prolonged unlawful occupation giving rise to a consolidated territorial situation. One in which bilateral dealings with the occupying power on matters concerning the occupied territory directly reproduce and legitimise the control. Diplomatic engagement, like India undertook on behalf of its vessels, aimed at securing legal compliance – even where it involves accepting partial relief rather than universal – is analytically distinct from conduct that would reproduce or stabilise the unlawful situation itself.

Russia

Russia has allegedly shared satellite imagery with Iran to help identify potential US targets. While such conduct may not, in itself, amount to complicity under Art. 16 of ARSIWA, this assessment depends on the purpose for which the imagery is provided. If the imagery is shared exclusively to identify US-targets that are believed to constitute legitimate military objectives under Art. 52 (2) AP I and are attacked in the exercise of self-defence, no international wrongful act would be supported. However, this assessment might change if the satellite imagery were used, with Russia’s knowledge, to facilitate unlawful retaliatory strikes carried out outside of the scope of self-defence under Art. 51 of the UN-Charter. With regard to potential violations of the law of neutrality, the analysis is considerably more complex and lies beyond the scope of this article.

Spain

Spain’s conduct provides the sharpest contrast. Prime Minister Sanchez condemned the US-Israeli strikes as an “unjustified and dangerous military intervention” contrary to international law, and Foreign Minister Albares confirmed that the bases at Rota and Morón de la Frontera would not be used for anything beyond what the bilateral treaty permits or in ways inconsistent with the UN-Charter.

Reinforcing Rather Than Eroding International Law

For third states, the challenge today is to navigate international law in a manner that reinforces, rather than erodes it – even under intense strategic and political pressure. This requires not only military restraint, but also legal clarity: refraining from participation in unlawful uses of force, carefully limiting any defensive support and avoiding forms of logistical or military assistance that could enable and facilitate acts of aggression. The alternative is a world where the use of force is determined less by rules than by military and economic power, which is not a desirable outcome.