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Collective self-defence or just another intervention?

Some thoughts on Turkey allegedly sending Syrian mercenaries to Nagorno-Karabakh


Following the recent escalation between Azerbaijan and Armenia in the conflict over Nagorno-Karabakh, multiplying voices note that Turkey, Azerbaijan’s closest ally, has been sending not only its military but also Syrian mercenaries to fight at the frontline against Armenia (see here, here, here, and here) – an allegation which both Turkey and Azerbaijan have denied (see here). Notwithstanding the fact that many States have condemned this intervention and urged Turkey to stay out of the conflict (see here and here), this post examines the question of whether there could be a legal ground for Turkey’s actions.

The conflict about Nagorno-Karabakh

Nagorno-Karabakh is a disputed area on the territory of Azerbaijan currently under the effective military control of Armenia. After a full-fledged war between 1991 and 1994, Azerbaijan and Armenia signed a cease-fire (see here). Since then, the OSCE Minsk Group initiated several attempts in order to reach a peaceful solution to this conflict. However, none of these attempts was successful. To the contrary, multiple violations of the cease-fire took place since 1994, most recently in 2016.

On 27 September 2020, both parties resumed hostilities. Armenia, being the first to declare war (see here), reported that the hostilities began as Azerbaijan launched an attack against military positions of Armenia. Azerbaijan on the other hand stated it merely responded to Armenia shelling its army positions and settlements along the entire front line (see here). The fighting continued until 10 October, when a second cease-fire signed by Armenia and Azerbaijan came into effect (see here). After multiple reports of cease-fire violations on both sides (see here and here), the United States, Armenia, and Azerbaijan released a joint statement, announcing another cease-fire taking effect on 26 October (see here). Again, reports of cease-fire violations emerged just minutes after the agreement came into effect (see here).

Prior to the resumption of hostilities on 27 September, allegations arose that hundreds of Syrian fighters recruited by Turkey were transferred to Azerbaijan (see e.g. here), while Turkish officials stated that Turkey would support Azerbaijan’s right to self-defence (see here and here). As Turkey is not a belligerent party in the Nagorno-Karabakh conflict, the only possible ground of justification for its alleged interference is the one of collective self-defence.

Collective self-defence: looking back at Nicaragua

The “inherent” right to collective self-defence is recognized in Article 51 UN Charter as well as customary international law. The question was most famously dealt with by the International Court of Justice (ICJ) in its 1986 Military and Paramilitary Activities in and against Nicaragua (Nicaragua) decision. The United States argued that their actions carried out on behalf of El Salvador, Honduras and, Costa Rica against Nicaragua were justified on the ground of collective self-defence. The ICJ ultimately decided against the US: it did not find an armed attack by Nicaragua that could have triggered such a right to self-defence.

In Nicaragua, the Court identified three requirements for the existence of a right to collective self-defence. First, there must be an armed attack against a member State. Second, the State under said attack must declare to be the victim of an armed attack and, third, request the help of another State. The additional criteria of necessity, proportionality, and of a reporting obligation to the Security Council do not determine the existence of a right to self-defence, but rather whether the act of self-defence was carried out in accordance with international law. Non-compliance with one of the latter criteria would, therefore, constitute an additional ground of wrongfulness.

Does Turkey meet the criteria set out in Nicaragua?

When determining the existence of an armed attack against Azerbaijan, the first problem arising is one of evidence. While there is evidence that both States launched attacks against one another, both Armenia and Azerbaijan blame the other party for initiating the conflict. As argued on this blog before (see here), none of the incidents in late September were able to meet the high threshold of an armed attack, although by now, the ICJ’s “scale and effect” threshold (see here at 195) might arguably have been met. Alternatively, one could argue that, by occupying the Nagorno-Karabakh region and by continuously violating Azerbaijan’s territorial integrity, Armenia is still conducting an armed attack today. Indeed, the military occupation of another State’s territory is considered an act of aggression under customary international law, reflected in General Assembly Resolution 3314 (XXIX). Additionally, the Security Council issued four resolutions (see here, here, here and here) reaffirming the territorial integrity of Azerbaijan and demanding the immediate withdrawal of Armenia from all occupied areas of Azerbaijan. Hence, an armed attack is arguably (still) present.

Additionally, for the existence of a right to collective self-defence, a declaration and request by Azerbaijan, asking Turkey for aid in exercising the right to self-defence, is also required. As the ICJ emphasized in Nicaragua, “there is no rule in customary international law permitting another State to exercise the right of collective self-defence on the basis of its own assessment of the situation.” Azerbaijan, in multiple letters addressed to the UN Secretary-General, declared it was under an armed attack by Armenia and invoked self-defence (see here and here). Moreover, Azerbaijan called on the United Nations and its Member States “to take decisive steps to force the aggressor Armenia to comply with international law and bring it to account” (see here). Regarding the relations between Azerbaijan and Turkey, a 2010 Agreement on Strategic Partnership and Mutual Support (see here) governs the defence cooperation between the two States. It includes that the countries will help each other if either one invokes its right of self-defense under Article 51 UN Charter. This cooperation agreement in addition to Azerbaijan’s declarations and calls for “decisive steps” strongly indicate that both the declaration and request criteria have indeed been fulfilled.

Consequently, the existence of Turkey’s right to collective self-defence in the present conflict is not prima facie unrealistic. However, this does not mean that Turkey’s actions constitute a lawful exercise of collective self-defence, especially considering that Article 51 UN Charter sets out additional criteria to this end. Indicatively, Turkey has disregarded the obligation to immediately report to the Security Council (see here at 145). Furthermore, Turkey has openly declared that the newest cease-fire was merely a “temporary solution” and that it would continue to support Azerbaijan on the battlefield. By violating the cease-fire and not striving for a permanent and peaceful solution, Turkey exceeded the limits of necessity and proportionality.

The role of the Security Council and the OSCE Minsk Group

Under Article 51 UN Charter self-defence is allowed until the Security Council takes “measures necessary to maintain international peace and security”. It is questionable whether the Security Council resolutions and the referral of the conflict to the OSCE Minsk Group qualify as measures triggering this “until clause”. While the resolutions are binding under Article 25 UN-Charter (see here at 113), they are not enforceable, as no reference to Chapter VII was made therein. The Security Council opted for a referral of the conflict to the OSCE Minsk Group, instead. The OSCE is a regional organization that operates without a binding treaty. Hence, it has no competence to impose sanctions. The efforts put forth by the Minsk Group, including the temporary cease-fire, have shown not to be effective. The crucial question is whether the “until clause” is triggered once the Security Council takes any action (regardless of its nature or success) or once it takes effective action under Chapter VII. The text of Article 51 is open to both interpretations. Considering the drafting history and the inherent character of the right to self-defence, a narrow interpretation is more convincing (cf. here with further references). Following the narrow interpretation, the referral of the conflict to the OSCE was not convincing and that further measures by the Security Council would have been necessary.

Concerning the legality of mercenaries

Most of all, a worrying question that remains is the implication of Turkey (allegedly) sending foreign mercenaries to Azerbaijan. According to Armenia, this constitutes a violation of “numerous international legal norms, which are binding, including for Azerbaijan and Turkey” (see here). Indeed, under the International Convention Against the Recruitment, Use, Financing and Training of Mercenaries, to which Azerbaijan is a State party (see here), using mercenaries in a conflict is prohibited. Turkey, on the other hand, is not bound by the said Convention. Under International Humanitarian Law, mercenaries do not enjoy the status of combatant or prisoner of war (see here) and using them is not prohibited. Hence, there is no indication that the use of mercenaries per se constitutes a violation of international law for Turkey.

Ella Schönleben
Ella Schönleben is a PhD candidate at the Institute for International Law of Peace and Armed Conflict (IFHV). She works as a research associate at Ruhr-Universität Bochum’s Center for International Affairs (ZfI) and the Chair for Public Law, incl. European Law, International Law and International Economic Law.
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1 Kommentar
  1. Dear Ella,
    Thanks a lot for this insightful and well-researched article! I enjoyed reading it a lot, especially since you presented multiple legal perspectives on this important issue. While I was reading your piece, a few question came into my mind:
    First, it seems like you were a little bit reluctant to admit that Turkey may lawfully exercise collective self-defense. You argued that there is evidence for the existence of an armed attack and that Azerbaijan has asked Turkey for military support. Therefore, it came as a counter climax when you qualified Turkey’s actions as unlawful on the grounds that it didn’t notify the UNSC and that its use of force is unnecessary and disproportionate. I wonder how you arrive at the latter conclusion. You said that Turkey’s actions are unnecessary and disproportionate because it violated the ceasefire agreement and is not striving for a permanent solution. Necessity is usually understood as leaving a state no other options to respond to an armed attack. What alternatives do you think Turkey and Azerbaijan have? And proportionality generally relates to the size, targets, and duration of the attack and self-defense. How do you assess that Turkey’s and Azerbaijan’s actions were out of scale in relation to the Armenian aggressions. Was the alleged self-defense retaliatory or merely intended to repel possible future attacks?
    Second, if Turkey and Azerbaijan are violating art. 51 read together with art. 2(4) of the Charter what would the consequences be? Especially if you keep in mind that the prohibition on acts of aggression is regarded as a peremptory norm of general IL. Does the international community have a responsibility to intervene in this conflict and stop the violation?

    I’d be really interested in your take on these issues! Thanks a lot!

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