The Legality of the Downing of the Turkish Drone by the US

On 4 October 2023, the US downed a Turkish drone in Syria after it came within 500m of a US military base in a region controlled by Syrian Democratic Forces (SDF) in eastern Euphrates. Multiple Turkish drones carried out airstrikes in the region as part of a response to a terrorist attack aimed at the Turkish Interior Ministry in Ankara. Some initial strikes were within a so-called restricted operating zone (ROZ), which the US claimed as a security buffer to protect its troops. Afterwards, one drone re-entered the zone and approached where US forces were deployed. Before the incident, Turkish officials were contacted several times, informed about the presence of the US troops in the proximity, and warned that forcible measures would be taken in self-defence if the drone did not leave. In the end, the US decided to act and downed the drone. No US forces were harmed, and there was no indication that Turkey intended to strike US targets. The facts are not disputed publicly by Turkey. The US explicitly stated that it acted in self-defence.

This incident, involving a hostile confrontation between the two largest standing military forces of the North Atlantic Treaty Organization (NATO) alliance, requires an assessment of the legality of the use of force. It also marks the first-ever instance of the downing of a military aircraft between two NATO members. Despite the political and legal implications of the event, it has been overlooked by the international law blogosphere.

The first issue that arises is whether the US forces stationed in Syria are entitled to use force in self-defence. The second issue relates to the non-existence of any direct harm against the US military that triggered a response by the US. Therefore, the self-defence claim must be assessed by considering whether any action by Turkey can lead to a lawful act of anticipatory self-defence by the US.

Lacking an invitation by the Syrian government, the US presence in Syria still rests on the original justification letter of collective self-defence on behalf of Iraq as well as the wider goal to ‘defeat ISIS in designated areas of Iraq and Syria, and [set] conditions for follow-on operations to increase regional stability’ and therefore, arguably on shaky grounds. However, the US’ right to self-defence does not depend on the legality of its military presence in Syria. As regulated under Article 51 of the UN Charter, States are entitled to use force in self-defence ‘if an armed attack occurs’. This formulation neither necessitates the armed attack to occur in the attacked State’s territory nor excludes military personnel positioned in third States (Ruys, p. 200).

Accordingly, the legality of the downing of the drone directly relates to the question of whether it falls into the scope of the right to self-defence. Although it can be claimed there was a threat to the US military base due to the military activity in its vicinity, the existence of a threat is not equal to an actual armed attack. While the restrictive approach to the right of self-defence emphasises the wording of ‘if an armed attack occurs’ and requires an actual armed attack that takes place, the permissive approach focuses on its broader customary rule and allows the use of force against future attacks (Ruys, p. 250). Although the latter approach was broadly rejected by the international community initially, post-9/11 practice shows that a considerable number of States – including the US and Turkey – and scholars accept the legality of self-defence against imminent armed attacks (Gray, p. 170). Still, many States and scholars continue to deny the possibility of any kind of anticipatory self-defence (Green, p. 106). As an in-depth discussion on this debate is beyond the scope of this blog post, we will limit the assessment to whether the downing of the drone can be justified under the permissive approach.

Anticipatory self-defence permits States to act when there is sufficient certainty of an imminent attack. In other words, there must be ‘a reasonable level of certainty that [the imminent armed attack] will occur in the foreseeable future’ (Lubell, p. 718). Accordingly, if the existence of the threat was derived from an imminent armed attack against the US, it could defend itself under anticipatory self-defence.

The incident occurred inside a US ROZ, an aerial security zone where the operation of other ‘airspace users is restricted’ (here, p. A-5), and which was announced to Turkey. An aircraft flying in the zone can arguably be classified as a potential threat by the US and shot down accordingly. However, this does not offer a direct justification under the law on self-defence. The US practice supports this: not even the actual attacks conducted earlier in the zone against SDF were answered by the US. Only after coming within 500m of its forces, heading towards the US base, and thus even closer than earlier, did the US deem the drone as ‘a potential threat’ and down it. The question is, then, whether the proximity and direction of the drone are sufficient to accept an imminent attack. The details of the incident indicate otherwise.

After the downing, the Pentagon stated that there was no indication that Turkey was about to target US forces intentionally. Thus, the assessment by the US must have been that there was an imminent risk of unintentional targeting. This can happen under three circumstances: first, if Turkey was unaware of the US military presence; second, if there was an anticipation of a mechanical malfunction of the drone; or third, if Turkey was about to conduct an imprecise drone strike close to the US base. Considering self-defence against unintentional armed attacks is possible (Henderson, p. 215), the downing of the drone can be justified under anticipatory self-defence if any option was the case.

The facts show that the first possibility can be ruled out. First, the statement of the Turkish foreign affairs minister, which predates the Turkish operation and recommends third parties (implying the US) to ‘stay away from the facilities and people belonging to the PKK and [their Syrian wing] the YPG’, shows that Turkey was aware of US presence in the region. Second, the US informed Turkey about the location of the base via ROZ notification. The second possibility seems inapplicable to the case since there is no indication that the US expected any harm due to a malfunction. Instead, the fact that the US asked Turkey to remove the drone indicates that there was no foreseen malfunction.

Consequently, the downing of the drone can only be justified under anticipatory self-defence if the drone was about to hit the US base because of an imprecise attack. If this was the case, the assessment of the US must have been that the proximity and direction of the drone substantiate an imminent imprecise attack that will harm the US accidentally or incidentally. Therefore, the question is whether there was ‘a reasonable level of certainty that [such an imminent armed attack] will occur in the foreseeable future’ (Lubell, p. 718). The US, claiming self-defence, bears the burden of proof of an (anticipated imprecise) armed attack (ICJ, para. 57). Yet, the US limited itself to emphasising the direction and proximity of the drone, and an anonymous military source revealed Turkey was warned beforehand.

The prior warning shows that the US was disturbed by the drone’s presence, and it is undisputed that the drone was there to conduct an attack against the SDF. Yet, the refusal to remove the drone from the area cannot be conclusive evidence of an imprecise attack. The earlier attacks show that Turkey was not only willing but also able to conduct its operation in the vicinity of the US base without harming the US forces.

The US’s emphasis on the proximity and direction of the drone shows that these factors were vital to the decision to shoot down the drone. It is true that a military drone operating near a military base and heading toward it will, in many contexts, be an indication of an imminent attack. Yet, the reason behind the Turkish drone’s presence is not disputed: to hit an SDF target. In this sense, an armed attack was indeed imminent. However, the compelling question remains: was there reasonable certainty that the attack would harm the US accidentally or incidentally? An affirmative answer could only be possible if the proximity and direction of the drone were perceived as preparation for an (imprecise) attack against a target near the base. The detailed information was withheld from the public and confined to the direction and proximity of the drone. Although there were targets in the area that Turkey could have attacked without harming the US, no evidence of an imminent and imprecise attack is provided. The US, relying on self-defence, should have established a reasonable level of certainty on an anticipated attack against a target that was near the base, and the potential for unintended harm to the US resulting from an attack on this target, yet failed to do so. To add to that, the past practices of Turkey show that it is surgical not to harm the US in its fights with third parties and, accordingly, avoid any such imprecise attack.

Consequently, since there is no sufficient proof of an imminent armed attack that would hit or harm the US accidentally or incidentally, the downing of the drone was not justified as an act of anticipatory self-defence. It seems more plausible that considerations of national military security were decisive for the downing – considerations that must be separated from international law regulating self-defence.