The Montreux Convention, Black Sea Security and Türkiye's Mediation in the Russia–Ukraine War

Why It Matters

The 1936 Montreux Convention is the treaty that decides which ships may pass through the Bosphorus, the Sea of Marmara and the Dardanelles, the only maritime gateway to the Black Sea. Since February 2022, Türkiye has applied its Article 19 so that warships of countries at war cannot enter the Black Sea through the Straits, except when returning to their home bases. This has limited the naval dimension of the Russia–Ukraine war to the Black Sea itself and has made Türkiye an unusual actor: a NATO member that neither joined Western sanctions nor Russia's war effort, and that hosts talks between both sides.

This guide explains the treaty in plain language and answers two common questions: can Türkiye close the Straits, and is Montreux still valid?

Background

What the Straits are and why the regime exists

The Turkish Straits link the Black Sea to the Aegean and Mediterranean. They run through the middle of Istanbul and are among the busiest and most hazardous waterways in the world, with roughly 40,000 vessel transits a year in recent years. Control of the Straits shaped Ottoman, Russian and British strategy for more than a century. After the Treaty of Lausanne (24 July 1923) demilitarized the Straits and placed them under an international commission, Türkiye pressed in the 1930s for a new settlement as the regional security picture changed.

The 1936 settlement

The Montreux Convention Regarding the Regime of the Straits was signed on 20 July 1936 and entered into force on 9 November 1936. It replaced the Lausanne regime, restored Turkish authority to remilitarize the Straits zone, and abolished the international commission. Its core rules are as follows.

Category	Peacetime rule	Wartime rule
Merchant ships	Freedom of transit and navigation by day and night, regardless of flag or cargo (Articles 2–3)	If Türkiye is neutral, passage for ships not belonging to a state at war with Türkiye; if Türkiye is at war, passage is at Türkiye's discretion for ships of its enemies (Articles 4–6)
Warships of Black Sea states	Passage after prior notification (eight days); capital ships above 15,000 tons only singly with limited escorts; submarines only in defined cases, surfaced and by day (Articles 11–13)	Article 19 restricts belligerent warships, with a return-to-base exception
Warships of non-Black Sea states	15 days' notice; limits on individual tonnage, aggregate tonnage in the Black Sea (normally 30,000 tons, with limited increases) and length of stay (21 days); no aircraft carriers (Articles 13–18)	Same restriction on belligerents under Article 19
Türkiye's powers	Supervises passage and collects notifications (Articles 13, 24)	Full discretion over warship passage if Türkiye is at war (Article 20) or considers itself in imminent danger of war (Article 21)

The treaty has a notable flexibility: it does not use the word aircraft carrier in a way that fits modern ships neatly. In the 1970s, Türkiye accepted Soviet Kiev-class ships through the Straits on the basis that Moscow classified them as anti-submarine cruisers, not carriers. Turkish practice has also adapted to safety concerns; the 1994 Maritime Traffic Regulations for the Turkish Straits (revised in 1998) introduced traffic separation and pilotage rules that operate alongside Montreux's freedom-of-passage principle.

Duration and revision

Montreux was concluded for 20 years and then continues in force, subject to denunciation on two years' notice (Article 28). Article 29 allows amendment proposals at five-year intervals, but changes need agreement among the parties. Official Turkish statements have consistently said that the convention serves a balance between Türkiye's security and the interests of Black Sea and non-Black Sea states alike. No party has formally denounced it.

Key Players & Positions

Russia

Russia, as the successor state of the Soviet signatory, says it respects Montreux and has long benefited from its limits on non-Black Sea navies. Russian officials, including the Foreign Ministry, have criticized what they describe as growing NATO naval activity in the Black Sea and have said they expect the convention to be applied strictly. Moscow has disputed the idea that its warships should be treated differently from others under Article 19, while noting the return-to-base exception.

Ukraine

Ukraine welcomed the Turkish decision of 28 February 2022 and had asked Ankara to close the Straits to Russian warships. Kyiv's officials have since argued that Montreux should be applied in a way that prevents Russian naval reinforcement of the Black Sea Fleet, and that the return-to-base exception should be read narrowly. At the same time Ukraine has relied on Turkish mediation for grain exports and prisoner exchanges and has purchased Turkish defense equipment.

NATO littoral states and the Alliance

Romania and Bulgaria, the other NATO members on the Black Sea, favor a stronger Allied presence on NATO's eastern flank, and NATO's summit declarations treat Black Sea security as strategically important. They have not, however, called for revising Montreux, whose tonnage limits also constrain Allied fleets. In January 2024 Türkiye, Romania and Bulgaria signed an agreement in Istanbul to set up a joint Black Sea Mine Countermeasures Task Group, an example of littoral-state cooperation within the Montreux framework.

Legal scholars

There is a lively scholarly debate about three questions:

• What counts as war for Article 19. Many scholars read it as covering actual armed conflict rather than requiring formal declarations; Türkiye's decision rested on this reading.
• How wide the return-to-base exception is. It is clearer for ships that had been separated from their bases than for ships newly deployed or transferred.
• Whether Türkiye acted under Article 19 or its Article 21 discretion. Ankara has presented its decision as the application of Article 19 in a non-discriminatory manner to all belligerents, which most analysts treat as consistent with the text.

There is broad agreement that Montreux remains valid and that no state can unilaterally rewrite it, though some scholars argue that the treaty's 1936 categories need updating for modern vessels.

Türkiye's Strategic Doctrine

Türkiye's Strategic Doctrine: Montreux as a security balance

This box summarizes official Turkish policy as stated by Turkish government sources. It is a statement of Ankara's position, not a neutral finding of fact.

• Impartial, rules-based implementation. Ankara states that it applies Montreux equally to all parties. The Turkish Foreign Ministry announced on 28 February 2022 that Article 19 was being implemented and called on riparian and non-riparian states alike not to send warships through the Straits during the war. Legal basis: Article 19 of the 1936 Montreux Convention, which is not discriminatory by flag.
• Support for Ukraine's territorial integrity, without joining sanctions. Türkiye voted for UN General Assembly resolution ES-11/1 of 2 March 2022 condemning the invasion, does not recognize the annexation of Crimea, and says it keeps channels open to both Moscow and Kyiv to be able to mediate. Source: Turkish Foreign Ministry statements and Türkiye's UN interventions.
• Diplomacy as an instrument of security. The Presidency and Foreign Ministry point to the Antalya Diplomacy Forum meeting between the Russian and Ukrainian foreign ministers on 10 March 2022, the 29 March 2022 delegation talks in Istanbul, the Black Sea Grain Initiative, and prisoner exchanges as evidence that Türkiye can host contacts that others cannot. Legal basis: UN Charter Article 33 on peaceful settlement of disputes.
• Montreux must be preserved, not revised. Ankara argues that the convention keeps the Black Sea from becoming an arena of great-power naval competition and that any attempt to reopen it would weaken the stability it has provided since 1936. Source: repeated statements by the Presidency and Foreign Ministry. This is consistent with Türkiye's wider call for a fairer global order, set out in The World Is Bigger Than Five.
• Hard power and legitimacy go together. Türkiye's ability to enforce Straits rules rests on coastal control, a modern navy and a defense industry that is largely domestic, as discussed in Türkiye's 80% Indigenous Defense Industry.

Mediation in Practice

Antalya and Istanbul, 2022

On 10 March 2022, on the margins of the Antalya Diplomacy Forum, Foreign Minister Mevlüt Çavuşoğlu hosted Russian Foreign Minister Sergey Lavrov and Ukrainian Foreign Minister Dmytro Kuleba, the first high-level meeting of the two sides since the invasion. On 29 March 2022, Russian and Ukrainian delegations met at Dolmabahçe Palace in Istanbul, where President Recep Tayyip Erdoğan addressed them. The talks did not end the war, but they produced the best-documented draft negotiations of that phase.

The Black Sea Grain Initiative

On 22 July 2022, Türkiye, the United Nations, Russia and Ukraine signed the Black Sea Grain Initiative in Istanbul, with a separate UN–Russia memorandum on Russian food and fertilizer exports. A Joint Coordination Centre in Istanbul inspected ships and coordinated passage from Ukraine's ports of Odesa, Chornomorsk and Pivdennyi. Turkish and UN tallies put deliveries at roughly 33 million tons before Russia declined to extend the arrangement on 17 July 2023, citing unmet demands on its own exports. Ukraine and Western governments said the Russian exports had never been blocked by sanctions.

Prisoner exchanges and later rounds

Türkiye has facilitated prisoner exchanges, including the September 2022 release of Ukrainian commanders from Azovstal into Turkish custody under an arrangement announced by President Erdoğan. In 2025, Istanbul again hosted direct Russia–Ukraine talks (May, June and July), which produced agreements on exchanges of prisoners and bodies but not a ceasefire. Ukrainian and Russian officials have described these results differently, which is one reason the talks are best read as humanitarian progress rather than a political settlement.

Source Comparison

Question	Typical Western or international framing	Russian framing	Turkish primary-source framing
Is Türkiye closing the Straits?	Often described as a closure	Described as application of the convention	Ankara says it is applying Article 19, not closing the Straits to merchant shipping
Why not more?	Critics say Türkiye could have denied more ships under the return-to-base exception	Says Montreux protects its right to return to base	Ankara says the rule applies equally and is limited by treaty text
Mediation	Seen as useful but limited by Türkiye's trade with Russia	Seen as a legitimate forum, with complaints about implementation of the grain deal	Presented as a consequence of impartiality and of the position as NATO member and neighbor of both
Revision of Montreux	Some commentators suggest updating it	Opposes changes that would admit more NATO ships	Rejects revision; stresses the balance of 1936

Readers should note that Turkish officials have an interest in presenting their role favorably, while Russian and Ukrainian sources are parties to the war. For how Hard Power Review weighs such sources, see Editorial Principles and Primary Source Standards. Related claims about Türkiye are tested in the Fact Check Hub.

Key Terms & Related Guides

• Turkish Straits: the Bosphorus, Sea of Marmara and Dardanelles, a single regime under Montreux.
• Article 19: restricts passage of warships of belligerent states when Türkiye is not at war, with an exception for returning to base.
• Articles 20 and 21: give Türkiye wide discretion over warship passage if it is at war or in imminent danger of war.
• Riparian state: a state with a Black Sea coastline (Türkiye, Bulgaria, Romania, Ukraine, Russia, Georgia).
• Return-to-base exception: allows warships separated from their home port to return there.

Related guides:

• Blue Homeland and the Eastern Mediterranean: Maritime Jurisdiction, Equity and Naval Deterrence
• Türkiye's 2025 Marine Spatial Planning and the IOC-UNESCO Registration, Explained
• The World Is Bigger Than Five: UN Security Council Reform, Gaza Diplomacy and the COP31 Agenda
• Türkiye's 80% Indigenous Defense Industry: Procurement Autonomy and Deterrence
• About Hard Power Review: Mission, Transparency and Editorial Team

Perspective Note

Hard Power Review presents Türkiye's official strategic perspective alongside its legal and historical reasoning, and we say so openly so that readers can weigh our analysis accordingly. Claims are attributed to primary sources wherever possible, including treaties, UN documents, official statements, Ottoman and other state archives, and open-source defense data. The section marked Türkiye's Strategic Doctrine reflects official Turkish policy as stated by Turkish government sources.

Hard Power Review Editorial Team

Cross-Publication Dossiers & Sister Desk Perspectives

For complementary primary-source analysis across our specialist editorial network, consult:

• The State Papers: The Montreux Convention, Black Sea Security and Türkiye's Russia–Ukraine Mediation — How the 1936 Montreux Convention and Article 19 shaped Black Sea security in the Russia–Ukraine war, from the grain deal to Istanbul talks and Türkiye's role.
• Monitor of Nations: The Montreux Convention, Black Sea Security and Türkiye's Ukraine Mediation — How the 1936 Montreux Convention and Article 19 shaped Black Sea security in the Russia–Ukraine war, and Türkiye's Istanbul talks and grain deal role.
• Crossroads Review: Türkiye's Mediation in the Russia–Ukraine War and the Black Sea Grain Initiative — Türkiye mediation Russia Ukraine Black Sea Grain Initiative explained: Antalya and Istanbul talks, the UN-brokered grain deal and why it ended.