Can Turkey Close the Turkish Straits to Russian Warships?

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Following the recent Russian military intervention in Ukraine, Ukraine officially requested Turkey to shut the Turkish Straits to warships pursuant to the 1936 Montreux Convention. While the initial reaction of the Turkish government implied the unwillingness of Ankara, the President of Ukraine put further pressure on Turkey to close the Straits with his recent statement, which was initially understood as the announcement of an agreement with Turkey on the closure of the Straits, which was swiftly denied by the Turkish authorities. (here and here). However, later on Sunday the Turkish minister of foreign affairs announced that “It is no longer a military operation, but a state of war,” and they will apply the Montreux Convention accordingly, both to Russia and Ukraine.

The Turkish minister of foreign affairs had previously claimed that there would be no practical effect of possible closure since Russian warships would still have the right to return to their bases. Although it is not clear how the Ukrainian side interprets the Convention, it can be presumed that they expect certain practical outcomes -unlike the Turkish side. In this post, I will therefore address the legal question of whether the 1936 Montreux Convention entitles Turkey to close the Turkish Straits to Russian warships.

A Brief History

The Turkish Straits did not make the headlines for the first time in the context of Russian military activity. In the aftermath of the conflict between Russia and Georgia in 2008, it was Russia who depended on the Montreux Convention to criticise the presence of military vessels of NATO allies in the Black Sea. A similar controversy regarding the presence of US warships arose between Turkey and Russia in the aftermath of the (illegal) annexation of Crimea in 2014.

In fact, the issue of the Turkish Straits has been an important part of the Black Sea geopolitics for centuries, and the passage of warships has been regulated by international treaties at least since the 1833 Treaty of Hünkar İskelesi, signed between the Ottoman Empire and Russian Empire. Under a secret article of the Treaty, the Ottomans accepted closing the Strait of Dardanelles (Strait of Çanakkale) to foreign warships, except for the Russian warships. When the terms of the Treaty were published in the British press in the following months, other European powers, Britain and France in particular, officially protested and sent their warships to the Aegean Sea. Following the end of the 8-year term of the Treaty, it got replaced by the London Straits Convention of 1841, which prohibits non-Ottoman warships from passing the straits during peacetime. This rule was preserved in the subsequent treaties until the Lausanne Straits Convention in 1923, which accepted extensive freedom for the passage of foreign warships. Eventually, the Montreux Convention was signed in 1936, following the diplomatic initiative of Turkey, due to her security concerns.

The Legal Regime of the Turkish Straits under the 1936 Montreux Convention

The Montreux Convention regulates the passage of foreign vessels through the Turkish Straits, consisting of the Strait of Dardanelles, the Marmara Sea and the Bosporus (Strait of Istanbul). The Convention provides separate rules for merchant vessels and warships and stipulates different regimes for peacetime, wartime -Turkey being belligerent, and wartime- Turkey not being belligerent. Lastly, there are provisions regarding the times when “Turkey consider herself to be threatened with imminent danger of war.” (Article 21(1))

The peacetime regulation regarding merchant vessels provides “complete freedom of transit and navigation in the Straits” (Article 2(1)) while certain -relatively minor- restrictions are accepted for other times. On the other hand, the regime regarding the passage of warships is rather detailed and restrictive. Therefore, certain privileges have been granted to the riparian States of the Black Sea to ensure their security.

The transit passage of warships, during peacetime, is limited in terms of technical features, tonnage, gun calibres, etc. and requires prior notification of Turkey. Furthermore, the Convention provides that the warships of the non-riparian States of the Black Sea are not allowed to “remain in the Black Sea more than twenty-one days, whatever be the object of their presence there.” (Article 18(2))

On the other hand, when Turkey becomes belligerent in a war, complete authority over the passage of warships is given to Turkey. The same authority is accepted, as a rule, when she considers herself to be threatened with imminent danger of war, except for the warships that are separated from their bases which are entitled to return thereto. However, if the warships that are separated from their bases belong to the State whose attitude threatens Turkey, she can deny the right to return to them. Nevertheless, the Council of the League of Nations (the Turkish doctrine widely argues that this should be read as a reference to the UN Security Council today) can decide, by a two-thirds majority, that the measures taken by Turkey are not justified. In this case, Turkey must discontinue the relevant measures.

Lastly, during wartime -Turkey not being belligerent, warships of non-belligerent States are subject to peacetime regulations. In contrast, “Vessels of war belonging to belligerent Powers shall not, however, pass through the Straits … Notwithstanding … 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.” (Article 19) In any case, obligations under the Covenant of the League of Nations (the Turkish doctrine widely argues that this should be read as the UN Charter today) and treaties of mutual assistance binding on Turkey are accepted as exceptions.

Is it Possible to Close the Turkish Straits to Russian Warships on the basis of the Ongoing Conflict?

Considering Turkey is not a belligerent party to the ongoing conflict between Russia and Ukraine, Turkey must either consider herself to be threatened with imminent danger of war or depend on the existence of a war between Russia and Ukraine for a possible closure of the Straits to Russian warships.

Regarding the first possibility, it is apparent that Turkey is not under a threat of an imminent danger of war. Nevertheless, the Convention gives complete discretion to Turkey to make the relevant decision. Therefore, in strictly legal terms, it is possible for Turkey to consider herself to be threatened with imminent danger of war. In this scenario, Turkey would be entitled to deny passage to the warships, including the Russian warships that are separated from their bases -since the attitude of Russia is the reason behind the closure. Arguably, the only legal procedure that Russia could apply is taking the issue to the UN Security Council (as the successor of the Council of the League of Nations), if expecting the support of the two-thirds majority as required by Article 21(4) of the Montreux Convention.

However, two legal considerations make this scenario unrealistic (along with several political considerations that fall outside the scope of this blog post). First and foremost, it is apparent that Turkey does not consider herself to be threatened by an imminent danger of war. Although the ongoing conflict between Russia and Ukraine may change the geopolitics of the Black Sea and endanger certain interests of Turkey, these considerations cannot be equal to an imminent danger of war, and a false declaration regarding Turkey’s position would be against the principle of good faith and amount to a violation of the Convention. Second, Turkey would risk the denunciation of the Convention, which she considers an essential legal apparatus for the security of the Black Sea, by Russia per Article 28 of the Convention.

Regarding the second possibility, what must be determined is the meaning of ‘war’ for the purposes of the Convention and whether the ongoing conflict is a war. Although it can be claimed that the term war should be understood as international armed conflict (IAC) today since States do not declare war anymore, the practice implies that no State claims that Turkey can close the Straits to warships during any IAC. In this direction, the possibility of the closure of the Straits was never mentioned during the conflicts between Russia and Georgia in 2008 and Russia and Ukraine in 2014. Furthermore, it should be acknowledged that not all conflicts between States were classified as war under international law in the 1930s. Accordingly, an interpretation that equates the term war with the term IAC would be broader than the parties intended.

War, in legal terms, starts with a declaration of war. (here, at 32) Accordingly, it is accepted that “There may, therefore, be a state of war without the use of force or after the use of force has ceased, or there may be the use of force without a state of war. The physical results of the use of force may be the same in all cases, but the legal results are clearly distinguished.” (here, at 328) Furthermore, Article 1 of the 1907 Hague Convention (III) relative to the Opening of Hostilities (both Russia (since 1909) and Ukraine (since 2015) are parties to the Convention) provides that a declaration must be made before the commencement of a war. However, in the present case, Russia did not declare war; instead, the Russian President described the ongoing military activities as a “special military operation,” which is clearly not a legal classification.

Nonetheless, as stated by Wright, “… a state commits acts of war on a large scale, but with repeated assertions that it is not intending to make war, is it possible for its acts to speak louder than its words? It is believed that such a situation may become a state of war, but only if recognized as such by the victim or by third states.” (here, at 365) Although Ukraine did not make a formal declaration of war, the fact that the Ukrainian President designated the ongoing conflict as war and announced they severed all the diplomatic relations with Russia -a traditional result of the existence of a state of war- is a sign that Ukraine, as the victim, might be recognised the ongoing conflict as a war. Yet, considering the President of Ukraine identified the capture of the Chernobyl Power Plant by Russian forces as “a declaration of war against the whole Europe,” his usage of the term war may be seen as a political statement rather than a legal classification as well. Still, the statement of the Ministry of Foreign Affairs of Ukraine is clearer and explicitly defines Russian military activities as an act of war. Furthermore, the Ukrainian request for the closure of the Straits can also be an indication of their legal classification. Regardless, an explicit declaration of war is missing until now.

On the other hand, the Turkish position seems more straightforward. On 25 February, it was explicitly stated by the Turkish minister of foreign affairs that they did not declare the ongoing conflict as a war, and Turkey continued to apply the peacetime regime under the Montreux Convention. However, on 27 February, the Turkish presidential spokesmen labelled the ongoing conflict as an “unjust and unlawful war.” Eventually, the Turkish minister of foreign affairs announced that Turkey formally declared the ongoing conflict as a war, and the relevant provisions of the Montreux Conventions will be applied to the warships of Russia and Ukraine. So, the question remains: considering Turkey declared that there is a war between Russia and Ukraine, can she close the Straits to Russian ships?

As explained earlier, if Turkey is not belligerent, the Montreux Convention only allows Turkey to close the Straits to the warships of the belligerent parties, i.e., Russia and Ukraine. Consequently, it is possible for Turkey to close the Straits to Russian warships (along with the Ukrainian warships) if it accepts the existence of a legal state of war. However, the exception provided by the Convention should be taken into consideration as well. Accordingly, the warships that are separated from their bases have the right to return thereto. Turkey must allow Russian ships to return their bases even if she closes the Straits to them otherwise.

Nevertheless, the meaning of the term ‘base’ is not provided by the Convention. Therefore, it can be argued -with a very restrictive interpretation- that the fact that Russia has bases that are located outside the Black Sea may entitle Turkey to refuse the Russian warships’ passing through the Straits by directing them to alternative bases. In other words, a very narrow interpretation of the right to return may treat it as a remedial right that entitles a passage through the Straits only if there is no alternative base to return for the warships. However, this interpretation would be in contradiction with the past practices regarding the Montreux Convention. For instance, during WWII, Turkey, not being a belligerent party, did not allow the passage of the Black Sea Fleet of the Soviet Union through the Straits, despite the existence of the Russian bases outside the Black Sea and the Soviet Union accepted this practice. Two important conclusions can be derived from this practice. First, the term base does not mean any base but means the base that a warship belongs to -which means Turkey cannot direct a warship to an alternative base. Second, the closure to warships cannot be paralysed by changing the base of a warship to abuse the right to return. Therefore, in case of closure, only warships that belong to a base in the Black Sea can enjoy the right to return.

Consequently, the answer to the posed question should be affirmative; the Montreux Convention entitles Turkey to close the Turkish Straits to Russian warships since there is an ongoing war between Russia and Ukraine, Turkey not being belligerent.

However, this closure would not be effective as much as possibly expected due to the right to return, which is explicitly recognised by the Convention itself. Accordingly, in case of closure, Turkey would be under an obligation to allow the return of the warships of the Russian Black Sea Fleet, if they are separated from their bases. Furthermore, there is no time limit regarding the presence of the warships of the riparian States of the Black Sea, unlike warships of the non-riparian States. Therefore, the Russian warships that already passed the Straits into the Black Sea (see here and here) can stay there as long as they wish, which only lessens the possible effects of the closure. The only practical effect of the closure would be that Russia would no longer be allowed to bring into the Black Sea further warships belonging to its other fleets, i.e. those not themselves based in the Black Sea, which will likely not matter much for the ongoing hostilities.

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Marco Longobardo says

February 28, 2022

Thank you for the post.

I believe that Turkey can close the straits under the MC.

However, I also believe that the MC could not be in any case a barrier.

As I mentioned Sat on Twitter, Russia is committing violations of erga omnes obligations (e.g., ban on aggression). Turkey can violate the Montreux Convention in countermeasure.

Plenty of authors (e.g. Picone, Tams, Sicilianos, Proukaki, Dawidowicz) say that "lawful measures" that can be undertaken by non-directly injured states in cases of violations of erga omnes obligations refers to countermeasures which are lafwul violations of PIL. The opposite view (that this refers to retaliations) would render Article 54 devoid of meaning (states would be authorised to do what is already lawful).

Indeed, most sanctions are countermeasures for violations of erga omnes obligations. Ask yourself the legal basis of sanctions against Russia (Crimea and Ukraine), Libya (before UNSC) and Syria, which violated previous agreements or CIL rules. The only source of legality is countermeasures by non-directly injured states.

There is also the possibility to argue that under the duty to cooperate to bring to an end violations of groos violations of jus cogens, Turkey must close the straits (thanks to Eliav Lieblich for the suggestion). I believe that Turkey (alike other states) has a due diligence obligation to do something, but that this something is not specified. However, closing the straits would be a good way to demonstrate that Turkey acted diligently.

This is not to detract from the conclusions that the MC allows to close the straits, but to stress that Turkey could do that also if the MC didn't allow so.

However, I see why Turkey may be reluctant to confront Russia on that, as stressed by Nilufer Oral in a blogpost today:


Ferhat Ercümen says

February 28, 2022

Thank you, Emre for this excellent take on the lex specialis regime of the Turkish Straits under the Montreux Convention. But I also would like to add that the Convention text does not say Turkey may or may not close the straits to belligerent parties' warships but instead, it reads as “Vessels of war belonging to belligerent Powers shall not, however, pass through the Straits…" So, what Turkey had to do (and has done rightly) was to execute the necessary and objective (if such a thing exists in treaty interpretation) application of the Convention text based on the factual reality (state of war).

Prof Nilufer Oral also has just posted on her blog the implementation of the Art. 19 of the Montreux Convention in the current conjuncture. In her blog post, she hints at the possibility (but quite unlikely) of even denying the Art. 19(4) exceptions to belligerent parties in case of violations of peremptory norms according to the ILC's draft conclusion 19(1) and 19(2). I think the combination of your and Prof Oral's post depicts a quite elucidative picture from a legal perspective. Thanks again.

Mary Ellen OConnell says

February 28, 2022

Dear Emre,

Let me add my compliments to Ferhats, but also to point to UN Charter Article 51. Turkey may join with Ukraine in using military force against Russia in collective self-defense.

That entitles Turkey to also take measures short of armed force, including countermeasures as defined in ASR Article 22. Turkey may violate Russia's rights under the Montreux Convention in response to Russia's prior violation upon notice of its reason for doing so, and so long the measures are necessary and proportionate.

Given the magnitude of Russia's breach of the prohibition on the use of force, closing the Straits to its shipping is a modest step.

I am assuming the EU's closure of airspace to Russia, which violates the Chicago Convention, is based on the same legal analysis.

The General Assembly can also act to recommend and coordinate collective countermeasures during its Emergency Special Session.

Thank you,

Mary Ellen