Clouds of War Over the Persian Gulf – A Jus ad Bellum Analysis (Part II)

Clouds of War Over the Persian Gulf – A Jus ad Bellum Analysis (Part II)

[Mohamed S. Helal is an Assistant Professor of Law at the Mortiz College of Law and an Affiliated Faculty with the Mershon Center for International Security Studies. This is the second part of a two-part post; the first can be found here.]

Second: Resisting Iranian Regional Policies and Responding to Indirect Iranian Aggression

The U.S. National Defense Strategy states that “Iran is competing with its neighbors, asserting an arc of influence and instability while vying for regional hegemony, using state-sponsored terrorist activities, a growing network of proxies, and its missile program to achieve its objectives.” America’s allies, especially Israel, Saudi Arabia, Bahrain, and the UAE, probably share this assessment. These countries cite Iran’s relations with Hezbollah in Lebanon, its presence in Syria and its support of President Bashar Al-Assad, its influence in Iraq, its connections to the Houthis in Yemen, and its alleged intervention in the affairs of its Arab neighbors, as evidence of its destabilizing regional policies. These countries could argue that these policies, and Iran’s support of non-state actors throughout the region, are forms of “indirect aggression” that justify an armed response. Indeed, Secretary of State Mike Pompeo has stated that “the fact that those actions take place, if they do, by some third-party proxy, whether that’s a Shia militia group or the Houthis or Hezbollah, we will hold the Iranians — Iranian leadership — directly accountable for that.”

Under the current lex lata of international law, only states can commit acts of aggression and the right of self-defense can only be exercised against an armed attack attributable to a state. “Indirect aggression” is a doctrine that governs the use of force in self-defense against non-state actors. Assuming that the acts of non-state actors meet the thresholds of gravity and scale, the doctrine of “indirect aggression” requires a high degree of dependence between a non-state actor and its state-sponsor to permit the use of force against the latter in response to the acts of the former. For the acts of non-state actors, such as the Houthis or Hezbollah, to be attributed to a state, such as Iran, the relationship between the two must satisfy one of two standards:

(1) De Facto State Organ: One possibility is that the relationship of dependence and the degree of control between the state and non-state actor is such that the latter becomes a de facto organ of the state. According to the ICJ (Genocide Convention Case para. 392), to satisfy this standard, the non-state actor must “act in complete dependence” on the state to the point that it becomes “merely the instrument” of the state.

(2) Substantial Involvement in the Acts of a Non-State Actor: U.N.G.A. Resolution 3314 on the Definition of Aggression refers to cases of the “substantial involvement” of a state in the acts of non-state actors, thereby permitting the use of force in self-defense against that state. The question of what forms of state support of non-state actors satisfy the “substantial involvement” threshold is a controversial question in jus ad bellum. In the Nicaragua Case (para. 195), the ICJ declared that “assistance to rebels in the form of the provision of weapons or logistical or other support” does not constitute an armed attack that permits the exercise of self-defense. Instead, the Court categorized such acts as unlawful uses of force or acts of intervention. Later ICJ jurisprudence, especially the Advisory Opinion on the Wall and the Armed Activities in the Congo Case, appear to reaffirm the restrictive approach of the Nicaragua Case, whichdoes not view the supply of arms, logistical support, or providing safe harbor to non-state actors as armed attacks. This position has been challenged by several dissents authored by ICJ judges and is the subject of thoughtful critiques by numerous scholars, especially in the U.S.

Ultimately, whether the acts of non-state actors can be attributed to Iran, and whether those acts amount to armed attacks depends on the facts of each particular case. Iran’s general regional posture or its overarching policy of supporting certain non-state actors cannot, taken cumulatively, constitute grounds for armed action. To justify war, a specific act by a specific non-state actor must be of sufficient scale and gravity, and must either be attributable to Iran or must be committed with substantial Iranian involvement. Iranian policies may, however, constitute violations of the prohibition on intervention in the internal or external affairs of states. That subject is beyond the scope of this blogpost, but I have examined the content and contours of the prohibition on intervention and proposed a novel understanding of the concept of coercion in a forthcoming article available here

Third: Naval Operations in the Persian Gulf and the Strait of Hormuz

The most likely situation that could trigger armed conflict in the Persian Gulf is an incident at sea. As the 1980-1988 Iran-Iraq war showed, the range of possible confrontations at sea is endless. A U.S. naval vessel might be harassed by the Iranian coast guard, an oil tanker might be struck by a mine that the U.S. or its Arab allies might claim was laid by Iran, a U.S. submarine or surface craft may intrude (intentionally or accidentally) into Iranian territorial waters provoking a forceful response, or Iran may threaten the freedom of navigation in the Strait of Hormuz. Obviously, I cannot here evaluate the legality of every potential contingency that might occur in the seas of the Persian Gulf. I will, however, identify and (again, very briefly) address the legality of two potential situations that may occur as tensions rise in the region.

(1) Attacks on Military and Merchant Vessels:

It is uncontroversial that naval military units, such as surface warfare vessels and submarines, are instrumentalities of the state, and as such, direct attacks on these units would constitute armed attacks justifying the use of force in self-defense. As the ICJ stated in the Oil Platforms Case (para. 72), “the mining of a single military vessel might be sufficient to bring into play the inherent right of self-defense.”

The legality of forceful responses to attacks on merchant vessels is slightly more complicated. It is generally accepted that a state may take measures to protect its merchant fleet and vessels flying its flag, such as by providing military escort to these vessels while traversing areas of conflict or tension. If, however, a merchant vessel is attacked the question becomes the nature and extent of the permissible response by the flag-state. It is probably uncontroversial to claim that if a merchant vessel being escorted by a military vessel comes under attack, the latter may use force to repel the ongoing attack. This would constitute a form of “unit self-defense” (see here).

The more difficult question is whether an attack on merchant vessels, or even a single vessel, entitles the flag-state to exercise a broader right of self-defense. Such a right could involve pursuing the vessels of the attacking state, intercepting attacks that have not yet reached their targets, and degrading the capability of the attacking state to mount further attacks against merchant vessels.

In my view, even a single attack on a merchant vessel entitles the flag-state to engage in self-defense against the attacking state through proportionate measures that are necessary to protect the flag-state’s merchant vessels. The flag-state is required, however, to demonstrate that the attacking state specifically targeted its merchant vessels. This view is based on the position of the ICJ in the Oil Platforms Case (for a critique of this case see Dominic Raab’s article). In that case, the U.S. accused Iran of attacking the U.S.-flagged vessel Sea Isle City in Kuwaiti waters. The Court was not satisfied that the evidence proved that the attack was attributable to Iran. Nonetheless, the Court noted that, putting aside the question of attribution, the evidence did not show that the missile that struck the Sea Isle City was “aimed at the specific vessel, but simply programmed to hit some target in Kuwaiti waters.” This suggests that the U.S. would have been entitled to exercise self-defense against Iran if it had proven to the satisfaction of the Court that an attack specifically targeted at a U.S.-flagged merchant vessel was attributable to Iran.

(2) Mine-laying in the Persian Gulf and the Strait of Hormuz  

Assessing the legality of the use of force in response to the laying of mines is challenging because, first, as Christine Gray notes (p. 427), the rules of self-defense against naval mines are underdeveloped, and second, because it is permissible under international law to use naval mines for military purposes. These include “access-denial/sea-denial operations” that impede an adversary’s access to certain areas of the sea (see here and here). A cardinal rule that governs the use of mines in naval warfare and which reflects what the ICJ called the “elementary considerations of humanity,” is the obligation of notification. A state that uses mines at sea, whether in times of war or peace, is required to identify their location for the benefit of neutral shipping and the general freedom of navigation. Therefore, the difficulty in evaluating the legality of using naval mines is that it entails balancing the right of a state to deploy naval mines for military purposes against the principles of the freedom and safety of navigation.

One way to identify cases in which the use of mines would constitute an armed attack justifying the use of force in self-defense is to examine the legality of laying mines in different areas of the sea. In this regard, it is generally recognized that a coastal state is permitted to place mines in its internal and territorial waters as a defensive measure against potential enemies or adversaries. Such a right is limited by the obligations of notification and preserving the right of innocent passage. Accordingly, if a state fulfills these obligations, it can be generally assumed that damage caused to foreign military or merchant vessels by mines in the internal or territorial waters of a coastal state would not amount to an unlawful use of force or armed attack. Similarly, a state may not, in peacetime, lay mines in the internal or territorial waters of another state. That would constitute an unlawful use of force and could amount to an armed attack, especially if it damages military or merchant vessels of the state against which the mines were laid.

A coastal state is also permitted to place mines outside its territorial waters. Because such an act interferes with the freedom of navigation, the state deploying the mines is required to provide notice of the location of these mines, maintain records of their location, and ensure the availability of alternative sea lanes. If a state complies with these obligations, its deployment of naval mines would, generally, comply with international law and damage caused to the military or merchant vessels of other states would not constitute an armed attack unlocking the right of self-defense.

However, if a state fails to comply with these obligations, its actions (namely, laying mines without providing notification and without identifying alternative routes) would violate the law of the sea. This would not, on its own, amount to an armed attack allowing for the use of force in self-defense. On the other hand, as discussed above, if the military or merchant vessels of a state are struck by a mine, and the flag-state of the damaged vessels demonstrates that its vessels were specifically targeted by the naval mines, that would constitute an armed attack permitting proportionate and necessary forceful measures in self-defense.  

The final, and perhaps most critical issue, is the freedom of navigation in the Strait of Hormuz through which over 20% of global oil production flows. The general rule is that coastal states, and indeed all states, are under an obligation not to threaten the freedom of navigation in international straits and not to impede transit passage through these maritime chokepoints. Coastal states, such as Iran, may, however, conduct access-denial/sea-denial operations in a strait like the Strait of Hormuz. One way that Iran could do this is by laying mines across the navigational routes in the strait. As two leading naval experts explain, “such actions impose extremely high, ongoing obligations on mine-laying States to ensure safe and convenient alternate routes” through the strait.

The challenging question is whether a state, such as the U.S., may resort to force against an attempt to suspend or impede transit passage in the Strait of Hormuz. As a general matter, suspending the right of transit passage or preventing navigation through an international strait, whether through active naval operations or the more passive process of laying of mines, is not, on its own, an armed attack that allows the use of force in self-defense. Rather, such actions violate the law of the sea. Nonetheless, seafaring states, such as the U.S., would be entitled to take measures to ensure the continued freedom of navigation through the strait. Thus, for instance, the U.S. would be permitted to conduct mine-sweeping operations to clear mines placed in the strait. As mentioned above, it would also be permissible to provide protection to merchant missiles traversing the strait against attempts to impede the freedom of navigation.


The 2003 Iraq War was a senseless, needless war. It destabilized an already chaotic region, robbed millions of life and limb, and cost billions that could have improved lives in America and in Iraq. Unfortunately, it appears that the lessons of that war have not been learnt. The ongoing escalation in the Persian Gulf risks unleashing another war that could have untold ramifications on the Middle East and the world. This blogpost is, in essence, a call for restraint. By identifying some of the potential arguments for war and highlighting the strictly limited contingences in which the use of force would be lawful, my hope is to contribute to minimizing the likelihood of war.

After the end of World War I, German Chancellor Theobald von Bethmann Hollweg was asked why Europe had descended into the catastrophe of the Great War. He responded: “ah, if we only knew.” The leaders of Iran, Israel, their Arab neighbors and the U.S. would do well to heed the echoes of regret and remorse in von Bethmann Hollweg’s words.

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John Heieck

Mohamed, Not to be a stickler, but I disagree with the second part of your contention that “[u]nder the current lex lata of international law, only states can commit acts of aggression and the right of self-defense can only be exercised against an armed attack attributable to a state.” As you know, Article 51 of the UN Charter provides, in relevant part, that “[n]othing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations”. Conspicuously absent from Article 51 is language that an armed attack must occur “by a state” to trigger the right to self-defense. Thus, in order for your interpretation to be correct, you would have to add language to Article 51. The current jus ad bellum therefore arguably contemplates the right of states to exercise self-defense against non-state actors, a proposition which is expressly supported by, inter alia, UN Security Resolution 1373. And while UNSCR 1373 directly conflicts with the ICJ’s holding in the Armed Activities in the Congo (Uganda) case on this issue, I would argue that state practice supports the former over the latter. (Whether the SC (as the… Read more »