Türkiye’s Threats against Greece: A Violation of Article 2(4) of the UN Charter?

by | Sep 26, 2022

Turkey threats of force against Greece

On September 5-6, 2022, the Greek Foreign Minister Mr. Nikos Dendias sent letters to the EU, NATO, and the UN to bring to their attention public statements made by Türkiye’s President Recep Tayyip Erdogan whose “openly threatening nature and tone are more than obvious, thus dispelling any doubts as to their intended purpose.” More specifically, the letters refer to statements by President Erdogan that Türkiye could “come all of a sudden one night” and “What I’m talking about is not a dream … If what I said was that we could come one night all of a sudden (it means) that, when the time comes, we can come suddenly one night.” Such statements and a series of similar remarks are part of Türkiye’s political and military strategy towards Greece, signalling the possibility of military action. In this post, I will examine the question of whether they amount to a threat of force prohibited under Article 2(4) of the UN Charter and its customary counterpart.

Threats of Force

Article 2(4) of the UN Charter prohibits not only the use of force but also the threat of force in international relations. The reason is obvious. First, threats of force do not only have a destabilizing effect on international affairs, but they can also lead to the actual use of force. This is because a threat may be a prelude to the use of force if the threat does not yield the desired outcome. In fact, that force will be used is inherent in the very conduct of threatening with the possible use of force.

Second, a threat of force can provoke the threatened State to engage in a pre-emptive use of force because of miscalculation or in order to placate domestic public opinion. All this means that threats of force can endanger international peace and security.

The prohibition of the threat of force has been reaffirmed in international jurisprudence and practice (see Paramilitary Activities case, paras 187-190; the General Assembly’s Friendly Relations Declaration and Definition of Aggression resolution) and constitutes a customary law obligation. It has also been analyzed in international legal scholarship (see here and here p. 33-35). That having been said, the obligation not to threaten with use of force has been underused. This post clarifies its scope by examining (1) what constitutes a threat of force; and (2) when a threat of force violates Article 2(4) of the UN Charter.

According to a broadly accepted definition, a threat of force consists of a promise that force will be used if a certain demand is not met (p. 364). However, a threat does not qualify as a threat of force prohibited under Article 2(4) of the UN Charter unless the promised conduct amounts to an unlawful use of force (see Nuclear Weapons advisory opinion, para. 47). This means that a promise to use force in self-defense does not fall within Article 2(4)’s prohibition because the use of force in the exercise of the right of self-defense is lawful according to Article 51 of the UN Charter and customary law. That having been said, because the legal status of certain uses of force is uncertain (such as the use of force for humanitarian intervention or certain types of anticipatory self-defense), the lawfulness of corresponding threats could also be uncertain.

A threat of force can be explicit or implicit and conveyed through different means and methods (for example, statements, ultimatums, movement of troops, air surveillance etc. See the Independent International Fact-Finding Mission on the Conflict in Georgia Report). For this reason, the context within which threats unfold is very important. For example, military exercises against a background of severe tensions can be viewed as a threat of force. The recent Chinese military exercises around Taiwan can fall in this category if the 2005 Chinese Anti-secession law is taken into consideration as well as a host of other belligerent statements and acts by China. Likewise, Russia’s conduct towards Ukraine before the February 2022 invasion amounted to a threat of force. It was not only the particular statements, demands (see here and here), and Russian actions such as its military build-up that counted, but also the 2014 invasion and annexation of Ukraine.

Even an indication of small-scale uses of force below the threshold of Article 2(4), which the International Court of Justice characterized as “frontier incidents” or hostile acts such as military assistance to rebels (Paramilitary Activities case, paras 195, 227-228), may amount to prohibited threats of force depending on the context. According to the Guyana and Suriname Award of 2007, a warning issued by Surinamese gunboats to Guyana’s exploratory and drill ship C.E. Thornton to leave Suriname’s waters within 12 hours or face (unspecified) consequences constituted “an explicit threat that force might be used if the order was not complied with” (para. 439). What is important then is whether actions, statements or, in general, conduct assessed in context and under the prevailing circumstances demonstrate animus aggressionis.

An interesting question is whether, in order to fall within Article 2(4) of the UN Charter, a threat of force should always be contingent on a particular demand as the prevailing view maintains. In my opinion, this is one way that threats of force are conveyed but such an approach is quite narrow. It derives from the practice of coercive diplomacy where objectives were attained by threatening adverse consequences including the use of force. Coercive diplomacy was an alternative to military action and represented an improvement to international relations in an environment where the use of force was not prohibited.

However, the post-Charter international legal order is premised on the prohibition of the unilateral threat and use of force and on centralized and institutionalized mechanisms for the authorization of the use of force. The regulation of the threat and use of force now has its own rationale and autonomous standing. To the extent that a use of force can violate Article 2(4) of the UN Charter ipso facto even if it is not attached to a certain demand, the same should be true for threats of force since the legality or illegality of a threat of force depends on the legality or illegality of the projected use of force. If threats of force were to be prohibited only if they were attached to a particular demand, this would raise the threshold upon which threats of force become legally relevant.

Such a narrow understanding would have created a legal gap in the regulation of inter-State violence, increasing the risk of force being used (p. 35). To give an example, such an approach would not have captured Iran’s statement that Israel should be “wiped off the face of the earth” (see here and here p.10), which is nonsensical if the particular context where the statement was made is taken into account. That having been said, the link between the use and the threat of force does not mean that force needs to be used for a threat of force to become legally relevant. The prohibition of a threat of force is an inchoate prohibition to address the risk of force being used.

I, therefore, contend that Article 2(4) of the UN Charter prohibits threats of force irrespective of demands (specific or general), provided that they reveal an intent to use force and create a rational expectation in the mind of the targeted State that force will be used in the course of events, even if its timing or manner is not certain. What transpires from this is that the use of force need not be imminent to constitute an unlawful threat of force, although the imminence of the use of force may strengthen the argument that an unlawful threat of force exists and is important when determining the legality of any forcible reaction.

Türkiye’s Threats and the Prohibition of the Threat of Force

Returning now to the aforementioned statements by President Erdogan, in order to assess their lawfulness under Article 2(4) of the UN Charter it is important to consider the context within which such statements were made because, as I said, the determination that a threat of force exists is contextual.

The context is the differences between Greece and Türkiye regarding the extent of the territorial sea, exclusive economic zone (EEZ) and continental shelf in the Aegean Sea. In 1995, the Turkish Parliament adopted a declaration granting the Turkish government powers to use all means including military forces to safeguard the vital interests of Türkiye should Greece extends its territorial sea in the Aegean Sea from 6 nautical miles to 12 nautical miles (for the text see Tsagourias, “The Prohibition of Threats of Force”. See also Art 92 of Türkiye’s Constitution). That “casus belli” has not been withdrawn but was reaffirmed recently (see here and here).

Türkiye has also called into question Greece’s sovereignty over certain islands in the Eastern Aegean established by the Treaty of Lausanne of 1923 and the Paris Peace Treaties of 1947.

Furthermore, the phrase “we will come all of a sudden one night” used by President Erdogan seems to have a particular meaning indicating the use of force. He used this phrase in relation to Syria against which Türkiye conducted large-scale military operations in 2016, 2018, 2019, and 2020 and presently controls parts of Syrian territory. Türkiye has also conducted numerous cross-border operations in Syria, the latest in April 2022 (see here and here). President Erdogan said recently referring to Syria: “Like I always say, we’ll come down on them suddenly one night. And we must” (see here and here) which led the United States to warn against any offensive action (here and here).

It is not only President Erdogan but other members of his government such as the Foreign and Defense Ministers who use bellicose language and often refer to events which have particular meaning and significance to the parties. They invoke past wars and in particular the Turkish war of independence, which led to the defeat of the Greek Army in Asia Minor and the birth of the Turkish Republic under Kemal Ataturk.

These statements should also be assessed in conjunction with other acts which are, cumulatively, sufficient to indicate that the use of force is reasonably likely. I am referring here to overflights over Greek islands; violations of the Greek airspace and territorial sea; dog fights between Greek and Turkish fighter jets; and drilling in disputed areas.

Given the bellicose nature of the statements by Turkish officials, combined with the declared “casus belli” as well as Türkiye’s aggressive acts towards Greece and the hostile relations that currently persist between the two countries, the only reasonable inference from the sum of these concerted statements and acts is that Türkiye is threatening Greece with force. Türkiye has not put forward any legal justification to support its threats. Instead, the projected use of force is offensive and targets the territorial integrity and sovereignty of Greece. It therefore breaches Article 2(4) of the UN Charter. As was said, if the promised use of force is unlawful, the threat of force is likewise unlawful. Moreover, whatever the differences between the two States and the legal merits of their respective positions are, both are under an obligation to settle their disputes peacefully as stipulated by Article 2(3) of the UN Charter and customary law (see Friendly Relations Declaration) and not by using or threatening the use of force.

Response Options

How should Greece respond to Türkiye’s threats of force? First, Greece should use peaceful means to protect its rights and defend its sovereignty. It should bring the matter to the attention of international organizations such as the UN, the EU and NATO. It should employ other mechanisms of peaceful settlement such as negotiations, mediation, good offices, or referral to judicial settlement to which Greece is open as the Foreign Minister’s letter makes clear. Greece can also engage in what I referred to elsewhere as defensive counter-threats – for example, military exercises, deployment of troops and weapons, acquisition of modern weaponry. Such conduct does not breach Article 2(4) of the UN Charter because its aim is to signal Greece’s readiness to defend itself should actual force follows the threat of force and perhaps dissuade Türkiye from using force.

Can Greece use force in self-defense? This brings to the fore the concept of anticipatory self-defense. If Türkiye’s threat of force is a prelude to an imminent armed attack, Greece can act pre-emptively to defend itself. A lot depends on two conditions: first, the definition of an “armed attack;” and secondly, the construction of imminence. Regarding the definition of “armed attack,” the International Court of Justifies defines it as a grave use of force (Paramilitary Activitiescase paras 191-195) but there are States such the United States that make no such distinction and consider any use of force as giving rise to self-defense (see here para. Moreover, the assessment of gravity is context and reference based (see here p. 43-50). Regarding imminence, the question is whether it is construed in temporal terms when the attack is immediate according to the Caroline criteria or whether factual, military or other considerations are taken into account (here p. 59-65, here p. 222-228, and here). In my opinion, Greece should act at the last window of opportunity which would allow it to effectively defend itself against a foreseeable attack and this is not necessarily when the attack is about to occur.


This post has clarified the elements of a threat of force prohibited under Article 2(4) of the UN Charter and customary law by looking at the Greek-Turkish conflict. As was said, the prohibition serves an important purpose which is to minimize the risk of force being used. However, this aspect of Article 2(4) has been underused and for this reason its potential has been undermined. It is hoped that it will acquire the place it deserves, and States as well international organizations take it more seriously.


Nicholas Tsagourias is Professor of International Law at the University of Sheffield, UK.


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