On June 20, Iran sent a letter to U.N. Secretary-General António Guterres claiming that, just hours before,
a United States unmanned aircraft system . . . engaged in a clear spying operation . . . despite repeated radio warnings … entered into the Iranian airspace where the air defence system of the Islamic Republic of Iran, acting under Article 51 of the Charter of the United Nations, targeted the intruding aircraft [and destroyed it].
We will make no effort here to assess Iran’s factual claim, namely that Iran shot down the U.S. drone in its own airspace and not, as the United States asserts, in international airspace. Instead, we will examine Iran’s legal justification: that it destroyed the drone pursuant to Article 51 of the U.N. Charter. The June 20 letter suggests a subtle shift in Iran’s understanding of international law—one that may significantly increase the risk of escalation. We will analyze that rationale in light of Iran’s past legal positions, and consider some competing—and in our view less dangerous—legal justifications for shooting down intruding drones.
Article 51 recognizes “the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations.” During an earlier dispute with the United States, before the International Court of Justice, known as the Oil Platforms case, Iran accepted that the right of self-defense may be invoked only in response to an unlawful armed attack. Yet, in its recent letter, Iran never describes the alleged drone incursion—what it calls “a clear spying operation”—as an armed attack, or as an apparent prelude to one.
Instead, Iran describes the alleged incursion as a “blatant violation of international law and the Charter of the United Nations, in particular its Article 2 (4).” Article 2(4) of the Charter prohibits “the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.” Set aside whether the drone incursion, as alleged, violated Article 2(4). There is a deeper problem with Iran’s rationale: it is widely—though not universally—accepted, including by Iran not long ago, that not every violation of Article 2(4) triggers the right of self-defense under Article 51.
The text of the Charter suggests that States intended these different terms—use of force, armed attack—to carry different meanings. The International Court of Justice has held that only “the most grave forms of the use of force” constitute an armed attack and trigger the right of self-defense. Many States, perhaps most, have followed the Court’s lead. This approach creates an asymmetry: not every use of force can be met with force in response. This asymmetry is intended to serve a purpose: by limiting States to non-military responses to low-gravity uses of force, this view seeks to limit the escalation of conflicts that might be resolved without further violence.
In the Oil Platforms case, Iran accepted the Court’s view, stating that “the notion of armed attack triggering a right of self defence must be more narrowly construed than the notion of unlawful use of force in Article 2(4) of the Charter.” It seems hard to reconcile this view with Iran’s recent letter, which appears to claim that the alleged incursion, which caused no damage to Iran, not only violates Article 2(4), but also suffices to trigger the right of self-defense under Article 51.
It is possible that Iran’s position has simply changed, and that it now takes the view that any use of force constitutes an armed attack and triggers the right of self-defense. Iran’s statement in its Article 51 letter, that it “reserves its inherent right, under Article 51 of the Charter of the United Nations, to take all appropriate necessary measures against any hostile act violating its territory” suggests as much.
Ironically, in collapsing the distinction between uses of force and armed attacks, Iran would align itself with the United States, which has “has long taken the position that the inherent right of self-defense potentially applies against any illegal use of force.”
But a passing remark from Iran’s submissions in the Oil Platforms case might provide an alternative justification. There, Iran stated that “It is not necessary to evoke the right of self-defence to justify preventing persons (whether agents of another State or not), vehicles or aircraft from penetrating into the State’s territory.” Of course, Iran’s June 20 letter did just that. Perhaps the letter had an instrumental purpose, beyond legal justification alone. For one thing, the letter gave Iran an opportunity to accuse the United States of violating the Charter, to the Security Council itself.
It is, of course, up to Iran to reconcile its past statements with each other, and (more importantly) with the U.N. Charter. But the underlying legal question is significant in its own right. Among scholars and states, there seems to be agreement that a state may shoot down an unmanned, unarmed drone within its borders (at least given additional facts such as provision of notice if feasible). But there is no clear consensus on the legal basis for such an act.
One approach, which Iran seems to take in its letter, would be to consider such incursions as uses of force, to find—alongside the United States—no daylight between uses of force and armed attacks, and therefore to treat such incursions as sufficient to trigger the right of self-defense. Importantly, even if the right of self-defense is triggered, its exercise remains constrained by other legal rules governing the use of force. Iran has previously insisted on fairly narrow interpretations of necessity and proportionality—narrower, in some respects, than those of the United States.
In the Oil Platforms case, Iran insisted that “self-defence is limited to an ‘on-the-spot reaction’” to an ongoing armed attack. Once an attack is over, forcible reprisals are prohibited. Before an attack begins, anticipatory self-defense is strictly limited. With respect to proportionality, Iran’s past statements are inconsistent, first adopting the ‘functional’ approach that defensive force must not exceed the actual needs of self-defense, later adopting the ‘quantitative’ approach that “counter-force must not be excessive in relation to the first use of force.” Either way, only the source of the threat may be targeted. Hopefully, these other legal constraints would limit the scope of forcible responses to unarmed incursions, and avoid unnecessary escalation.
A second approach might do less violence to the text and purpose of the Charter, and provide less risk of escalation. Recall that Article 2(4) requires States to “refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.” One of us (Ingber), considers that, even if shooting down a drone over a state’s own territory constitutes a use of force, it is not one against the territorial integrity or political independence of any state. Such a use of force would violate Article 2(4) only if it were in some other manner inconsistent with the purposes of the United Nations. While such an inconsistency could arise, given additional facts, shooting down an unmanned surveillance drone within one’s own borders is not, as such, inconsistent with the purposes of the United Nations.
The other author (Haque), considers that these terms—territorial integrity, political independence, inconsistency with purposes—do not limit the scope of the prohibition, but instead underscore its breath. The harder question for Haque is whether a State’s use of force against intruding aircraft within its own borders takes place in its international relations (which the Charter seeks to regulate) or, instead, within its domestic jurisdiction (in which the Charter promises not to intervene). By the ordinary meaning of these terms, such uses of force could be fairly described either way. However, if the primary object and purpose of Article 2(4) was to prevent States from projecting force beyond their borders, then ‘intraterritorial’ force should generally fall within a State’s domestic jurisdiction rather than in its international relations. Alternatively, States may simply agree, through their practice, to interpret these terms accordingly.
Notably, other rules of international law may prohibit States from exercising domestic jurisdiction over certain persons and things within their territory—for example, rules concerning the immunities of state property, diplomats, or visiting armed forces. The legal fiction of extraterritoriality, antiquated though it may seem, expresses the idea that such persons and things must be treated ‘as if’ they remain within their own State’s borders. Arguably, then, ‘intraterritorial’ force directed at such persons or things by a State occur in its international relations, rather than within its domestic jurisdiction, and therefore implicate Article 2(4). Obviously, intruding aircraft enjoy no such immunity.
On either approach, it is not necessary to invoke the right of self-defense to justify shooting down an intruding drone. Doing so would not implicate Article 2(4), to which Article 51 is an exception. Again, other rules of international law—such as international human rights law, and treaties governing civil aviation—limit a state’s ability to use force within its territory. But, under either approach, States could justify actions that most view as obviously lawful—specifically shooting down an intruding drone—without claiming a broader and possibly escalatory right to use force in self-defense in response to any incursion, however slight, on their territory.