The Montreux Convention, the Black Sea 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 Bosporus and the Dardanelles, and it is the legal backbone of Black Sea security. When Russia invaded Ukraine in February 2022, Türkiye used the Convention's Article 19 to bar belligerent warships from the Straits, and then used its position as a neutral host to mediate on grain, prisoner exchanges and ceasefire talks. Understanding the treaty explains why a single country on the Black Sea's southern shore became a central channel between Moscow, Kyiv and NATO capitals.

Background

What the Turkish Straits are

The Turkish Straits consist of the Bosporus (about 31 km / 19 miles), the Sea of Marmara and the Dardanelles (about 61 km / 38 miles). They are the only maritime link between the Black Sea and the Mediterranean. Istanbul, a city of more than 15 million people, sits astride the Bosporus, which makes the Straits both an international waterway and a dense urban and environmental space.

From Lausanne to Montreux

The 1923 Lausanne Straits Convention demilitarized the Straits and placed them under an international commission. Türkiye argued through the 1930s that this regime no longer matched the security environment. The Montreux Convention, signed on 20 July 1936 and in force since 9 November 1936, replaced it. It abolished the international commission, restored Turkish control and allowed Türkiye to remilitarize the Straits, while preserving freedom of commercial navigation.

How the passage regimes work

Three design features matter most:

• Asymmetry in favour of riparian states. Countries with a Black Sea coast enjoy fewer restrictions than outside powers, and outside naval presence is capped in size and duration.
• Article 19. If Türkiye is not at war, warships of belligerent states may not transit the Straits. Ships returning to their home bases are the recognized exception.
• Articles 20 and 21. If Türkiye is at war, or considers itself threatened with imminent danger of war, it may decide on warship passage at its own discretion.

Chronology of the 2022–2025 period

Key Players & Positions

Russia

Moscow's stated position is that Montreux must be applied as written and that Russia, as a Black Sea state, retains its treaty rights, including the return-to-base exception in Article 19. Russian officials have criticized what they describe as attempts by NATO members to expand naval activity in the Black Sea. Russia ended its participation in the Black Sea Grain Initiative in July 2023, saying that the parallel memorandum on Russian food and fertilizer exports had not been implemented.

Ukraine

Kyiv asked Türkiye at the outbreak of the war to close the Straits to Russian warships. It has since stressed that Türkiye's measures must be paired with practical security for its ports and shipping. President Zelensky and Ukrainian foreign ministers have welcomed Turkish mediation on grain and prisoners while asking Ankara for greater pressure on Moscow. Ukraine also values Türkiye's repeated statements that it does not recognize the annexation of Crimea.

NATO and Western states

NATO officials, including Secretary General Jens Stoltenberg at the time, publicly acknowledged Türkiye's role in implementing Montreux and in the grain deal. Western governments have also pressed Ankara to align more closely with sanctions. US Treasury officials in 2023 and 2024 warned Turkish firms about secondary-sanctions exposure for trade with Russia. Romania and Bulgaria, as NATO Black Sea members, work with Türkiye on mine clearance and maritime security.

The United Nations

The UN Secretary-General and UN agencies co-signed the grain arrangements and staffed the Joint Coordination Centre in Istanbul, which inspected vessels and scheduled passage. UN figures put the volume moved under the Initiative at about 32.9 million metric tons. Turkish officials round this to more than 33 million tons. The difference is one of rounding and counting method, not of substance.

Israel, the Palestinian side and regional actors on Gaza

Israel's government rejects Turkish criticism of its conduct in Gaza and accuses Ankara of hosting Hamas figures. The Palestinian Authority and many Arab and Muslim-majority states welcome Turkish humanitarian and diplomatic engagement. Egypt, Qatar and the United States have been central mediators, and Türkiye has taken part alongside them in ceasefire diplomacy.

Source Comparison

Readers should compare treaty text, UN documents and official statements side by side. Figures such as grain tonnage vary slightly by source and counting method.

Key Terms & Related Guides

• Montreux Convention: the 20 July 1936 treaty governing transit through the Turkish Straits.
• Article 19: bars warships of belligerent states from the Straits when Türkiye is not at war, apart from returning to base.
• Riparian (littoral) states: Bulgaria, Georgia, Romania, Russia, Türkiye and Ukraine.
• Black Sea Grain Initiative: the July 2022 arrangement among Türkiye, Russia, Ukraine and the UN, coordinated through the Istanbul Joint Coordination Centre.
• Joint Coordination Centre: the UN-staffed body in Istanbul that scheduled and inspected grain vessels.

Related guides:

• The Global Anatomy: Türkiye's Perspective on Maritime, Legal and Security Affairs
• Blue Homeland and the Eastern Mediterranean: A Complete Guide to Türkiye's Maritime Jurisdiction
• Türkiye's 2025 Marine Spatial Planning and IOC-UNESCO Registration: What It Means Legally
• Türkiye's Defense Industry at 80% Domestic Production: From Bayraktar TB2 to KAAN
• Editorial Principles: How The Global Anatomy Separates Fact from Position

The Global Anatomy presents Türkiye's official perspective on the issues it covers alongside the legal and historical arguments supporting it. Claims are attributed to primary sources such as treaties, UN documents, archival records and official statements, so that readers can verify them independently.

Cross-Publication Dossiers & Sister Desk Perspectives

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

• 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.
• Hard Power Review: The Montreux Convention, Black Sea Security and Türkiye's Mediation in the Russia–Ukraine War — The Montreux Convention Turkish Straits Russia Ukraine war explained: Article 19, Türkiye's closure to warships, grain deal, mediation and what comes next.
• 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.