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To Close or Not to Close

The Closing of the Turkish Straits under Articles 19 and 21 of the 1936 Montreux Convention Regarding the Regime of the Straits


This analysis by Nilüfer Oral first appeared on the NUS-CIL blog and is a revised and updated version of the original text.


President Zelensky’s Request to Turkey to Invoke Article 19

On 24 February 2022, Ukrainian President Zelensky requested the Turkish Government to close the Turkish Straits for passage of Russian military vessels under Article 19 of the 1936 Montreux Convention Regarding the Regime of the Straits. The Turkish Government responded that under the same provision of the Convention it could not prevent Russian military vessels from returning to their bases. Confusion ensued subsequently when President Zelensky in a Twitter message expressed his profuse appreciation to President Recep Erdogan and the Turkish people for the decision to close the Straits under Article 19(2), which then Turkey denied to be the case. On 27 February the Turkish Foreign Minister announced that Turkey would close the Straits to Russian warships.

On 28 February Foreign Minister Mevlut Cavusoglu further warned all countries (whether bordering the Black Sea or not) not to send warships via the straits to the Black Sea during the Russia-Ukraine war.

Article 19

Article 19 of the 1936 Montreux Convention Regarding the Regime of the Straits provides that when Turkey is not “belligerent”, warships enjoy the rights of passage as provided for in Articles 10-18 (these provide the conditions for notification, tonnage, vessel type, and other requirements as preconditions for passage through the Straits). However, passage is denied under Article 19:

“Vessels of war belonging to belligerent Powers shall not, however, pass through the Straits except in cases arising out of the application of Article 25 of the present Convention, and in cases of assistance rendered to a State victim of aggression in virtue of a treaty of mutual assistance binding Turkey, concluded within the framework of the Covenant of the League of Nations, and registered and published in accordance with the provisions of Article 18 of the Covenant.”

There is, however, one caveat, that “[n]otwithstanding the prohibition of passage laid down in paragraph 2 above, vessels of war belonging to belligerent Powers, whether they are Black Sea Powers or not, which have become separated from their bases, may return thereto.” It should come as no surprise that the qualification allowing return of vessels to the bases was important to the former USSR during the negotiations of the Montreux Convention.

The question today is whether, in light of the Russian invasion of Ukraine, the Turkish government should treat the Russian Federation as a belligerent power under the Convention and close the Straits to Russian military vessels (see also here, here, and here). And if so, whether Russian warships would still be allowed to return to their bases in Crimea, thereby effectively negating any real effect to Article 19. It is clear that Russia, having engaged in an armed military attack against the territorial integrity and sovereignty of Ukraine, is a belligerent for purposes of the Montreux Convention. The Convention provides no definition of belligerent and does not require any preliminary “declaration of war” or other official act. The Hague Convention of 1907 qualifies “belligerents” broadly beyond armies to include militia and voluntary corps. Common Article 2 to the four 1949 Geneva Conventions applies in all cases of declared war or of any other armed conflict which may arise between two or more of the High Contracting Parties, even if the state of war is not recognized by one of them.

While the 1936 Montreux Convention was negotiated before the UN Charter and the development of modern international humanitarian law and refers to the League of Nations, and despite the possibility for revision of the Convention every 5 years after it had been in force for 20 years, it has been applied unamended for the past 86 years, developed through subsequent practice and interpretation.

The Russian Invasion of Ukraine and Article 19 of the Montreux Convention

Russia’s invasion of Ukraine has been condemned by individual States and NATO as an act of aggression in violation of the UN Charter. There is no need for a formal declaration of war. Herein lies the devil and Turkey’s quandary. Over the 86 years, Turkey had shouldered the responsibility of implementing the Convention, as well as protecting its own security interests and that of the Black Sea throughout periods of world war and intense Super power rivalry.

The 1936 Montreux Convention created a lex specialis regime for the Turkish Straits, falling under Article 35(c) of the 1982 United Nations Convention on the Law of the Sea. In 1935, invoking fundamental change of circumstances and defense concerns in face of a looming war, the Turkish government successfully convened a new conference, which in months’ time adopted the current text of the Montreux Convention. Importantly, Article 25 of the Montreux Convention transferred all functions of the International Commission established under the 1923 Lausanne Convention to the Turkish Government.

The preamble to the Montreux Convention provides an important starting point. It places the security interests of Turkey and the Black Sea at the heart of the implementation of the Convention.

“Desiring to regulate transit and navigation in the Straits of the Dardanelles, the Sea of Marmora and the Bosphorus comprised under the general term “Straits” in such manner as to safeguard, within the framework of Turkish security and of the security, in the Black Sea, of the riparian States, the principle enshrined in Article 23 of the Treaty of Peace signed at Lausanne on the 24th July, 1923;”

The Montreux Convention distinguishes between Black Sea and non-Black Sea powers, recognizing certain advantages to the former. The regime of passage for vessels of war depends on whether the relevant times are times of peace or times of war, and whether Turkey is a non-belligerent or belligerent, or considers itself to be threatened with imminent war.

In times of peace, the rights of passage through the Straits is recognized for all military vessels but subject to restrictions on the type of vessel, total tonnage, mode of passage, use of aircraft while in passage, notification requirements and duration for non-Black Sea military vessels. Moreover, the passage of aircraft carriers is prohibited at all times, although during the Cold War this prohibition would be challenged by the former USSR several times. Submarine passage is also prohibited except in the case of Black Sea Powers which have purchased, constructed or repaired submarines outside the Black Sea and only for the purpose of re-joining their bases. However, submarines must travel by day and on the surface, and pass through the Straits singly (Article 12).

Turkey retains discretion to regulate the passage of warships in two circumstances: in times of war, if Turkey is a belligerent (Article 20), and should Turkey feel threatened with imminent danger of war (Article 21). Since 1936, the Montreux Convention has weathered the challenges of World War II and some five decades of the Cold War. During most of WWII Turkey remained neutral and the Straits were closed to belligerent powers pursuant to Article 19. While this prevented the USSR from sending warships to the Mediterranean, the Allies also were unable to send warships into the Black Sea. The current request from Ukraine is quite likely the first time since World War II that Turkey would apply Article 19.

Over the decades Turkey has had to engage in a careful and calibrated implementation of the 1936 Montreux Convention against a backdrop of hot-and-cold politics. For Turkey, the Montreux Convention is more than a treaty regulating the passage of ships through the straits; it constitutes a vital strategic interest.

In time, Western powers would also appreciate the utility of the Convention to control Russian ambitions. At the end of WWII, Stalin made an about-face in the long-established USSR position in favour of restricted warship passage by demanding that the Montreux Convention be modified to allow Soviet warships free passage at all times. Not only did the USSR want to open the straits to warships of Black Sea states at all times and prohibit passage to non-Black Sea warships, but it also wanted joint control with Turkey over the Straits and to establish bases. The United States, once in favour of revising the Convention, responded by sending the battleship USS Missouri to Istanbul on 5 April 5 1946, marking the first time a US warship anchored in the Istanbul Strait. This was the start of the Cold War.

When NATO was established in 1949, Turkey was the only Black Sea NATO power. While a staunch ally of the West, Turkey was also under great pressure not to antagonize her immediate and powerful Soviet neighbour, especially following the 1962 Cuban missile crisis, which included a secret agreement by Kennedy to remove missiles from Turkey. During much of the Cold War, Turkey remained in the forefront of Super power politics.

Crimea, Sevastopol and the Duty of Non-Recognition

The Belovezha Accords of 8 December 1991 formally ended the USSR’s existence and created the Commonwealth of Independent States. The Russian Federation emerged as a new state that initially enjoyed close ties with the West. Ironically, in 1994 the Russian Federation joined NATO’s Partnership for Peace Programme. However, any hopes for peaceful Black Sea relations in the post-USSR period were dashed with the Russian invasion of Georgia on 8 August 2008 and in 2014 with Russia’s annexation of Crimea. The same year NATO-Russian relations were suspended.

Crimea and Russia’s cherished Sevastopol naval base and Black Sea Fleet were given to Ukraine under the 1991 Belovezha Accords. In 1997 Ukraine and Russia partitioned the Black Sea Fleet between themselves. Russia maintained control over most of the fleet and the right to use the port of Sevastopol for twenty years until 2017. In 2010, the two parties further agreed to extend the Russian navy stay in Crimea to 2042. In April 2014, following the annexation of Crimea, Russia unilaterally terminated the 1997 and 2010 agreements.

Turkey’s position on Russia’s annexation of Crimea is unequivocal as expressed by President Erdogan that “Turkey doesn’t, never will recognize the illegal annexation of Crimea”. In her recent EJIL blog, Diane Desierto writes the “Russian annexation of Crimea in 2014 led to the unequivocal and united position of the international community that this was an ongoing glaring illegality representing continuing serious breaches and violations of the Charter of the United Nations and international law (as reiterated in a long series of UN General Assembly resolutions, see among others here, here, and here).” In turn, this gives rise to the obligation of non-recognition under Article 41 of the International Law Commission’s 2001 Draft Articles on the Responsibility of States for Internationally Wrongful Acts (ARSIWA) for serious breaches of peremptory norms of general international law as affirmed by the International Court of Justice 2004 Wall Advisory Opinion.

Draft Conclusion 19 of the current work of the International Law Commission on peremptory norms of general international law (jus cogens) also provides that:

DC 19 (1) “States shall cooperate to bring to an end through lawful means any serious breach by a State of an obligation arising under a peremptory norm of general international law (jus cogens)” and

DC 19 (2) “No State shall recognize as lawful a situation created by a serious breach by a State of an obligation arising under a peremptory norm of general international law (jus cogens), nor render aid or assistance in maintaining that situation.”

Article 21

Article 21 represents an important safeguard for Turkish security. It recognizes Turkey has the discretion to apply the provisions of Article 20 and close the Straits to all warships (Black Sea and non-Black Sea) without itself being a Belligerent should Turkey feel threatened with imminent danger of war. But there are differences. Should Turkey exercise its discretion under Article 21 a notification must be sent to the Parties and to the Secretary General of the League of Nations. The Council of the League of Nations by 2/3rds and a majority of the Parties to the Convention must agree with the decision. Should this not be achieved, the only outcome is for Turkey to discontinue such measures, including those undertaken under Article 6 (e.g. imposing mandatory pilotage).

It is not clear that Turkey intends to invoke Article 21. However, this raises the question of how to implement the provisions relating to the now defunct League of Nations Council. Notably, the Resolution for the Dissolution of the League of Nations, adopted 18 April 1946, did not transfer any role to the newly established United Nations relating to the 1936 Montreux Convention.


On 28 February 2022, the Turkish government correctly decided that Russia’s invasion of triggered Article 19 of the Montreux Convention, treating Russia as a belligerent. However, with one caveat that Russian military vessels would be allowed to return their bases. While Turkey may be making a strategic interpretation of Article 19(2), legally this could be questioned. As an act of aggression against the territorial integrity of Ukraine, the annexation of Crimea would trigger Article 41 of the ARSIWA. In which case, the exception allowing a belligerent power to return to its naval base would not apply. What remains unclear, is whether the Turkish Government has officially invoked Article 21 to exercise its discretion to close the Straits to all warships going beyond. This would require more than a statement from the government but formal notifications.

Understandably Turkey is once more engaging in a careful geostrategic calibration to avoid a dangerous naval confrontation between Russia and Turkey, a NATO member, in the Black Sea.

Nilüfer Oral

Nilüfer Oral is Director of the NUS Centre for International Law. In 2016, she was elected by the UN General Assembly to the International Law Commission where she is co-chair of the study group on sea level rise in relation to international law. Among other responsibilities, she is the editor of the International Straits of the World series (Brill), and has written extensively on the Turkish Straits.

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