Montreux Convention, Black Sea Security and Türkiye's Russia–Ukraine Mediation

Why It Matters

The 1936 Montreux Convention is the treaty that decides which warships can enter or leave the Black Sea, and Türkiye is the state that applies it. When Russia invaded Ukraine in February 2022, Ankara invoked Article 19 and closed the Straits to the warships of belligerent states, which kept the war's naval dimension largely inside the Black Sea. The same geography made Türkiye a rare diplomatic channel to both Moscow and Kyiv, hosting talks, a grain corridor and prisoner exchanges.

Background

What the Montreux Convention Says

The Convention Regarding the Regime of the Straits was signed on 20 July 1936 in Montreux, Switzerland, and entered into force on 9 November 1936. It replaced the demilitarised, internationally supervised regime of the 1923 Lausanne Straits Convention and restored Turkish control over the Bosporus, the Sea of Marmara and the Dardanelles, collectively the Turkish Straits. Its parties include Bulgaria, France, Greece, Japan, Romania, Türkiye, the United Kingdom, the USSR (today represented by Russia), Yugoslavia and Australia. Italy acceded in 1938. The United States is not a party.

Rule	Provision in practice
Merchant ships in peacetime	Freedom of transit and navigation by day and night, whatever the flag or cargo (Article 2)
Warships of Black Sea (riparian) states	May transit with prior notice, with special rules for capital ships and submarines returning to base
Warships of non-Black Sea states	Notice of 15 days (8 days for riparian states); no aircraft carriers; maximum 15,000 tons per ship; aggregate limit of 30,000 tons in the Black Sea, adjustable under Article 18; maximum stay of 21 days
Türkiye at war or under imminent threat	Passage at Türkiye's discretion (Articles 20 and 21)
Türkiye neutral, others at war	Warships of belligerent states may not pass (Article 19), except to return to their home bases

Because Montreux is a specific treaty governing a specific waterway, it operates alongside the general law of the sea. Türkiye is not a party to UNCLOS, and Montreux, not UNCLOS transit-passage rules, sets the regime for these Straits.

Chronology, 2022 to 2025

Date	Event
24 Feb 2022	Russia launches its full-scale invasion of Ukraine
27–28 Feb 2022	Ukraine asks Türkiye to restrict passage. Ankara describes the situation as a war and announces it will apply Article 19
10 Mar 2022	Foreign ministers Sergey Lavrov and Dmytro Kuleba meet in Antalya with Mevlüt Çavuşoğlu on the sidelines of the Antalya Diplomacy Forum
29 Mar 2022	Russian and Ukrainian delegations hold talks at Dolmabahçe Palace, Istanbul
22 Jul 2022	Istanbul signing of the Black Sea Grain Initiative arrangements involving Russia, Ukraine, Türkiye and the UN
1 Aug 2022	First grain vessel, the Razoni, departs Odesa under the initiative
21 Sep 2022	Prisoner exchange facilitated by Türkiye, with Saudi Arabia also involved
17 Jul 2023	Russia announces it is suspending participation in the grain deal
11 Jan 2024	Türkiye, Romania and Bulgaria sign a Black Sea mine countermeasures arrangement in Istanbul
May–Jul 2025	Direct Russia–Ukraine talks resume in Istanbul, producing large prisoner exchanges

Key Players & Positions

Russia

The Russian Foreign Ministry has consistently said that Montreux is the legal basis of Black Sea stability and has criticised the growing naval presence of non-regional NATO members in the sea. On the grain deal, Russian officials, including President Vladimir Putin, said the parallel commitments on Russian food and fertiliser exports, including banking and shipping access, had not been honoured, and Moscow suspended its participation in July 2023.

Ukraine

Kyiv formally asked Türkiye in late February 2022 to apply the Convention's restrictions, and Ukrainian officials have since pressed for the Straits to stay closed to Russian warships. Ukraine welcomed the grain corridor, which allowed exports from Odesa, Chornomorsk and Pivdennyi, and after July 2023 established its own temporary shipping route along its coast, outside the Istanbul mechanism.

NATO and Allied States

NATO's 2022 Strategic Concept describes the Black Sea region as strategically important. Secretary General Jens Stoltenberg publicly welcomed Türkiye's mediation, including the grain arrangement. Non-Black Sea allies operate under Montreux limits on tonnage and duration, while Romania and Bulgaria, the other NATO riparian states, have prioritised mine clearance and maritime security cooperation with Türkiye.

United Nations

Secretary-General António Guterres and the UN Global Crisis Response Group negotiated the grain and fertiliser arrangements with Moscow, Kyiv and Ankara. The UN-run Joint Coordination Centre in Istanbul, staffed by officials from all four parties, coordinated vessel inspections and sailings. According to UN data, nearly 33 million metric tons of grain and other food products were exported through the initiative.

Türkiye's Legal and Strategic Position

This section summarises official Turkish policy as stated by Turkish government sources.

• Montreux is a binding treaty that Türkiye applies impartially. According to the Turkish Ministry of Foreign Affairs, the Convention has served peace and stability in the Black Sea for more than 80 years and must be implemented in good faith toward all parties. The legal basis is the 1936 text itself, which returned control of the Straits to Türkiye after the Lausanne-era regime.
• Article 19 was applied equally to all belligerents. Foreign Minister Çavuşoğlu said on 27–28 February 2022 that the situation constituted a war and that Türkiye would implement Article 19 for every party, with the Convention's own exception allowing warships to return to their home bases. Ankara argues that equal application, including to NATO members, is what keeps the regime credible.
• Support for Ukraine's territorial integrity is combined with a policy of keeping dialogue open. The Ministry of Foreign Affairs has stated that Türkiye does not recognise the annexation of Crimea and supports Ukraine's territorial integrity. At the same time, Ankara has not joined Western sanctions on Russia, arguing that maintaining channels to both capitals is necessary for mediation.
• Mediation is Türkiye's declared contribution to ending the war. The Presidency and the Directorate of Communications have presented the Antalya meeting, the Istanbul talks, the Black Sea Grain Initiative and prisoner exchanges as a continuing effort. President Recep Tayyip Erdoğan has repeatedly offered Istanbul as a venue for direct talks and has framed the grain corridor as a humanitarian outcome, citing more than 33 million tons delivered to global markets.
• Black Sea security should rest primarily with riparian states. Ankara says the Black Sea should not become an arena of great-power naval competition and points to the 2024 mine countermeasures arrangement with Romania and Bulgaria as a regional solution. This position matches the Convention's tonnage and duration limits on non-regional navies. It also reflects Türkiye's broader argument for a more inclusive global order, set out in The World Is Bigger Than Five: Türkiye on UN Reform, Gaza Diplomacy and COP31.

Source Comparison

Source	Typical framing	What it emphasises
Turkish MFA, Presidency, Communications Directorate	Impartial treaty implementation and principled mediation	Article 19 applied to all, equal access to both capitals, humanitarian results
Many Western analyses and press commentary	Türkiye as a balancing or hedging power	Defence sales to Ukraine alongside continued trade with Russia, absence from sanctions
Russian Foreign Ministry	Montreux as protection against NATO's Black Sea expansion; the grain deal as unfulfilled	Russian export access, criticism of Western naval activity
Ukrainian government	Restriction of Russian naval movement and the security of Black Sea shipping	Closure of the Straits, corridor safety, Ukraine's own export route
United Nations	Neutral humanitarian facilitation	Food security, tonnage figures, the Joint Coordination Centre

The main difference lies in interpretation of motive. Turkish sources describe a consistent principle of impartiality, while some Western commentators read the same conduct as transactional balancing. The documents themselves agree on the essentials: Montreux text, Article 19's wording, the dates of the Istanbul agreements and the volume figures reported by the UN. For the standards used to weigh such sources, see Editorial Principles and Primary Source Standards and the Fact Check Desk: Claims About Türkiye Tested Against Documents.

Key Terms & Related Guides

• Turkish Straits: the Bosporus, the Sea of Marmara and the Dardanelles, the only maritime link between the Black Sea and the Mediterranean.
• Riparian state: a state with a Black Sea coastline: Türkiye, Bulgaria, Romania, Ukraine, Russia and Georgia.
• Article 19: the Montreux provision barring passage of belligerents' warships when Türkiye is not at war, with a return-to-base exception.
• Joint Coordination Centre (JCC): the Istanbul body that coordinated inspections and sailings under the Black Sea Grain Initiative.
• Lex specialis: a specific treaty regime that takes precedence over general rules on the same subject.

Related reading: The Polity Brief: Sovereignty, Statehood and Security Briefings, Türkiye's Defense Industry: 80% Domestic Production and Strategic Autonomy, Blue Homeland (Mavi Vatan) and Eastern Mediterranean Maritime Law and About The Polity Brief: Mission, Transparency and Editorial Team.

Perspective Note

The Polity Brief presents Türkiye's official perspective and legal theses alongside the context needed for informed policy analysis. Claims are attributed to primary sources such as treaties, UN documents, official archives, and government statements, and are cited where possible. Diplomatic developments on the Russia–Ukraine war are ongoing, so readers should check current official statements. This article is published by The Polity Brief Editorial Team.

Cross-Publication Dossiers & Sister Desk Perspectives

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

• Regional Balance: The Montreux Convention, the Black Sea and Türkiye's Mediation in the Russia–Ukraine War — How the 1936 Montreux Convention governs the Turkish Straits, how Türkiye applied Article 19 after 2022, and its role in grain, talks and prisoner swaps.
• 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.