Gulf States and Iran: The Implications of Hosting Military Bases Under Jus ad Bellum and Jus in Bello (Part I)

[Chiara Redaelli is research fellow at the University of Geneva, Faculty of Law, and IHL/ICL expert for IDLO, Kyiv office. She is also co-editor in chief of the Journal on the Use of Force in International Law and co-chair of the IHL Progressive Development Platform of Ukraine. 

Antonio Bultrini is Associate Professor of International Law at the University of Florence, Visiting Professor at the Sant’Anna School of Advanced Studies (Pisa) and teaches the law of armed conflict for the Italian Air Force and Navy. He is a member of the International Law Association’s Committee on the Use of Force, part of the Multidisciplinary Network on Sanctions (MINOS) and a former official of the Council of Europe.]

The Factual and Legal Baseline: Armed Attack and Aggression

Since late February 2026, the United States and Israel have conducted sustained strikes on Iranian territory. The chronology of these operations makes clear that the campaign has involved coordinated strikes on nuclear, military, leadership, and civilian targets. The jus ad bellum arguments advanced by Washington, principally a theory of anticipatory self-defence against Iran’s nuclear program, have been strongly rejected by international legal opinion, which holds that the campaign does not satisfy the requirements of lawful (anticipatory) self-defence under Article 51 (see e.g. here, here, and here).

Iran has retaliated by striking Bahrain, Qatar, the UAE, Kuwait, and Saudi Arabia. Iranian officials have stated publicly that any territory or airspace ‘utilized to support aggressors’ is a legitimate target, and an Iranian letter to the United Nations Secretary General explicitly invokes the right of self-defence under Article 51 of the Charter. The Gulf states, for their part, have condemned Iranian strikes and pointed to attacks on civilian infrastructure as evidence that Iran is targeting them as states, not merely as hosts for US forces. The legal significance of that distinction depends entirely on the status of military bases, how they are used, and the Gulf states’ involvement in the military operations. The analysis that follows proceeds through four scenarios, each entailing distinct legal consequences. 

Scenario One: Closing the Bases 

Under jus ad bellum, Iran’s right to direct force against Gulf state territory depends on whether any conduct attributable to those states rises to the level of an armed attack within the meaning of Article 51 of the Charter. So long as the Gulf states have neither committed acts of aggression themselves nor authorized the use of their territory for offensive operations against Iran, no legal basis under the jus ad bellum exists for Iranian force to be directed at them. 

The law of neutrality ranks among the most ancient bodies of customary international law, finding its principal codification in the 1907 Hague Conventions V and XIII and subsequently absorbed into the framework of Additional Protocol I. Neutrality designates the distinct legal status of a state that stands apart from an armed conflict. The framework is structurally bilateral in its obligations: belligerent parties are bound to respect the territory of neutral states, while neutral states bear a duty to uphold their own neutrality by all available means. Article 5 of Hague Convention V, together with the corresponding provisions of Convention XIII (Article 8), makes explicit that this duty is not merely passive: the neutral state is required to actively resist any infringement of its neutral status. The neutral state’s entitlement not to be drawn into the consequences of a conflict it has not joined is the precise counterpart of its obligation to ensure that its territory is not exploited as an operational platform by any of the belligerent parties (see here and here).

For the Gulf states, formal neutrality is not a viable option. The UAE hosts Al Dhafra Air Base, one of the most significant US forward operating installations in the region; Qatar hosts Al Udeid, the operational hub for US Central Command; Bahrain is home to the Fifth Fleet; Saudi Arabia and Kuwait host a substantial Army and Air Force presence (see here). These basing arrangements are embedded in bilateral defence treaties. Under the law of neutrality, a state hosting a belligerent’s military bases cannot in practice discharge the obligations of formal neutrality, since doing so would require it to close those installations and intern the foreign forces. 

Under formal neutrality doctrine, Iran would be obligated to respect Gulf territorial integrity and could not lawfully direct any force against Gulf state territory or assets. The inviolability of neutral territory under Article 1 of Hague Convention V is unambiguous. Yet because the legal precondition, namely the effective enforcement of neutrality against the US military presence, is unrealistic in practice, any formal declaration of neutrality would be legally hollow and would not confer the immunities that neutrality promises. 

Should Iran use force against Gulf state territory notwithstanding a valid declaration of neutrality, the full framework of the jus ad bellum would be engaged on the side of the victim state. An armed attack against a neutral state that has in good faith severed its military entanglements and fulfilled its neutrality obligations would trigger that state’s inherent right of self-defence under Article 51 of the UN Charter.

Scenario Two: Use of the Bases to Support Military Operations

In this scenario US forces use the military bases located in Gulf states bases to support the war efforts, but no attack is launched directly from the bases.

Jus ad Bellum: Complicity, Countermeasures, and Self-defence

Article 16 of the Articles on the Responsibility of States for Internationally Wrongful Acts (ARSIWA) provides that a state which aids or assists another state in the commission of an internationally wrongful act bears international responsibility if it does so with knowledge of the circumstances of the wrongful act and if the act would be internationally wrongful if committed by the assisting state itself. Both conditions seem readily satisfied in the Gulf context. Assisting in an act of aggression is clearly internationally wrongful if committed by the state itself, inasmuch as it would violate Article 2(4) of the Charter. The Gulf states’ awareness of the wrongfulness of the US-Israeli campaign is, at this stage, difficult to contest. Inter alia, the near-universal condemnation of the strikes by international lawyers are sufficiently public and unambiguous. The ILC Commentary makes clear that the requirement of wrongful intent should not be deployed to permit states to evade responsibility in situations ‘where internationally wrongful acts are manifestly being committed’ (here).

The ILC’s requirement of a sufficiently direct connection between the assistance and the wrongful act is not without significance. Passive hosting of a foreign military presence under long-standing treaty arrangements is qualitatively different from actively consenting to strike planning or directing logistical support toward specific operations. The assessment of each Gulf state’s derivative responsibility will therefore be fact-sensitive, turning on the degree to which its territory and infrastructure have been woven into the operational architecture of the campaign against Iran. 

The finding of complicity under ARSIWA Article 16 would legitimize Iran, as an injured State, to invoke the international responsibility of the relevant Gulf states and to demand, in the first instance, cessation of the internationally wrongful conduct and, where appropriate, assurances and guarantees of non-repetition, specifically the termination of the material support and territorial facilitation currently extended to the US-Israeli campaign (Articles 30 and 42–43 ARSIWA). Beyond cessation, Iran may claim full reparation for injury caused by the complicit conduct (Articles 31 and 34 ARSIWA), encompassing restitution, compensation, and satisfaction (Articles 35 to 37). Where diplomatic avenues are exhausted or ineffective, Iran may resort to countermeasures under Articles 49 to 53 ARSIWA: non-forcible measures directed at the responsible Gulf state that would otherwise be contrary to Iran’s international obligations towards that state, for the purpose of inducing cessation of the wrongful act and compliance with the obligations of cessation and reparation.

Countermeasures are subject to important constraints under the law of state responsibility. They must be proportionate to the injury suffered (Article 51 ARSIWA), and may only be directed against the State responsible through the temporary non-performance of obligations owed to that State (Article 49). They may not involve the threat or use of force (Article 50(1)(a) ARSIWA), and the ILC Commentary confirms that forcible reprisals are not permitted. Iran’s remedial toolkit in Scenario Two is therefore robust but non-military: it encompasses diplomatic protest, the suspension or restriction of treaty obligations and other forms of economic or political pressure that qualify as countermeasures under Articles 49–52 ARSIWA, as well as recourse to international adjudication or arbitration where available. By contrast, any use of force against the Gulf states themselves would have to be justified, if at all, under Article 51 of the UN Charter, which preserves an inherent right of self-defence only “if an armed attack occurs” attributable to those states.

This conclusion has a necessary corollary. Even where a Gulf state bears derivative responsibility under ARSIWA Article 16, this does not strip it of its inherent right of self-defence under Article 51. The law of state responsibility and the jus ad bellum operate on distinct normative planes: complicity generates obligations of cessation and reparation, enforceable through non-forcible means, but does not license the injured state to use force in response. In the scenario under examination, any use of force by Iran against a Gulf state would constitute a violation of Article 2(4) of the UN Charter and, if of sufficient scale and effect, an armed attack triggering the right of individual self-defence under Article 51.

Jus in Bello: The Doctrine of Non-Belligerency

A related but analytically distinct question is whether Gulf state hosting of US military operations renders those states parties to the international armed conflict between the United States, Israel, and Iran. The answer is negative. Passive territorial authorization, however operationally significant, does not constitute direct participation in hostilities. 

During the 2003 invasion of Iraq, the Italian Parliament authorized the U.S.-led coalition to use Italian airspace and bases, even as the government insisted that Italy would contribute ‘neither men nor equipment’, and portrayed its stance as one of non-participation in combat while providing extensive logistical and territorial support. Germany followed a comparable policy without formally proclaiming a special status: Berlin allowed U.S. forces to use major bases such as Ramstein and Rhine-Main as transit hubs, and thousands of U.S. combat troops deployed to Iraq from German territory. 

At the time, the status of Italy and Germany was characterized as one of non-belligerency, namely an intermediate position between formal neutrality and full belligerence, in which a state departs from the strict obligations of abstention and impartiality without thereby acquiring the legal classification of a party to the conflict. This category may be understood as a deviation from the duties of abstention, prevention, and impartiality that falls short of belligerent status. The drafting history of Additional Protocol I indicates that the framework presupposes the existence of this intermediate category. Non-belligerency is in effect the only legally coherent posture available to a state hosting foreign bases and military personnel, since strict neutrality would require measures incompatible with that hosting relationship, including the freezing of belligerent assets and the internment of belligerent troops for the duration of hostilities.

Non-belligerency describes the status of a state that supports one party to an armed conflict without itself becoming a party to that conflict. Within the law of neutrality, this intermediate status represents a departure from the classical binary between strict neutrality and belligerency: the non-belligerent state waives the obligations of impartiality that neutrality ordinarily entails, while stopping short of direct participation in hostilities. The emergence of this third status addresses a structural inadequacy in the classical framework, which afforded states no lawful intermediate position between abstention and belligerency; non-belligerency fills that gap by accurately describing what states supporting a party to a conflict in fact do, without requiring them either to maintain the fiction of neutrality or to cross the threshold into co-belligerency (here). Recent state practice arising from the conflict in Ukraine lends empirical weight to the consolidation of this status: France, the Germany, and Italy, among others, have provided sustained military assistance to Ukraine without acquiring belligerent status or being treated as parties to the conflict.

Applied to the present scenario, Gulf states that permit the use of existing installations for United States military operations would most naturally occupy this intermediate position: they are neither formally neutral, given the depth and institutionalization of their existing defense relationships with Washington, nor belligerent in the legal sense, absent direct participation in hostilities. The conditions under which sustained and escalating support might displace that characterization in favor of co-belligerency, and the distinct question of state responsibility that arises regardless of party status, are addressed in the second part of this post, which you can find here.