By Bosphorus News Research Desk
Study: Managing Montreux: Turkey and the Russia-Ukraine War in the Black Sea
Institution: Carnegie Europe, Carnegie Endowment for International Peace
Date: July 1, 2026
Region / File: Black Sea / Montreux Convention and Russia-Ukraine War
Research note: Türkiye's application of the Montreux Convention has made Ankara the principal gatekeeper of Black Sea security, leaving Ukraine's European and NATO partners dependent on close engagement with Türkiye, according to a Carnegie Europe study by Thomas de Waal. The paper combines historical and legal analysis, open-source military and trade material, and interviews conducted in Türkiye in late 2025 and early 2026.
De Waal argues that Türkiye's policy rests on regional ownership led by Black Sea coastal states, the containment of military escalation and continued freedom of navigation for commercial shipping. Ankara has used the convention to prevent Russian warships from returning to their Black Sea bases while discouraging non-Black Sea NATO members from sending naval forces through the Turkish Straits.
The study describes this wider arrangement as "Montreux Plus," a term attributed to an unnamed Turkish official interviewed in November 2025. Under the reported understanding, Russia accepted restrictions on the return of its warships in exchange for non-coastal NATO states keeping their naval vessels outside the Black Sea. The claim is central to the paper's account of Turkish policy but is based on interviews rather than a published agreement or official document.
Carnegie says the restrictions imposed after Russia's full-scale invasion helped prevent an early reinforcement of Russia's Black Sea Fleet and contributed to Ukraine's ability to defend Odesa and later weaken Russian naval forces. The same policy also limited direct NATO naval support for Ukraine, reflecting Ankara's preference for de-escalation and coastal-state control over a wider alliance presence.
The paper examines Türkiye's mine countermeasures cooperation with Romania and Bulgaria, an operational framework that has since widened into the protection of critical undersea infrastructure, alongside proposals for an Istanbul-based Maritime Component Command.
Turkish officials cited in the study say naval platform contributions to the planned command would be limited to Türkiye, Romania and Bulgaria, although other countries could contribute in different forms.
Strategic relevance: The study places Türkiye at the center of any postwar Black Sea security arrangement. The Montreux Convention gives Ankara control over access by warships, but de Waal argues that Türkiye has extended this legal authority through political understandings with Russia and NATO states.
This role is already visible in the Türkiye-Romania-Bulgaria framework, which now extends beyond mine countermeasures into the surveillance of cables, pipelines and other critical assets on the seabed.
A maritime force intended to protect Ukrainian ports or enforce a future ceasefire cannot be designed independently of Türkiye's interpretation of Montreux. Carnegie therefore recommends strengthening the naval capacity of Romania and Bulgaria and supporting Türkiye's ambition to lead the maritime component of a future coalition, rather than attempting to build a larger non-coastal NATO naval presence.
The study also identifies Russian shadow-fleet tankers as an area where Western and Turkish interests could overlap. De Waal argues that Türkiye has an environmental interest in inspecting older and potentially unsafe vessels passing through the Straits and may have legal room to apply tighter sanitary and safety controls.
Bosphorus News reading: Carnegie's strongest contribution is its description of Montreux as an active security-management instrument rather than a treaty Türkiye applies mechanically. Ankara is using the convention to determine which outside powers may enter the Black Sea, how far NATO can expand its naval role and what form a future ceasefire force could take.
The reported "Montreux Plus" arrangement deserves caution. The paper attributes the term and its details to an unnamed Turkish official, and no formal text is presented. It should therefore be treated as an informed account of an unwritten political understanding, not as a verified agreement with defined obligations.
The paper is more persuasive when examining warship access than when assessing civilian Russian shipping. Türkiye's policy of keeping commercial passage open follows a different legal and economic logic from its restrictions on naval vessels. Combining Russian shadow-fleet traffic, sanctions enforcement and Montreux risks obscuring the distinction between wartime naval controls and the broader international regime governing merchant shipping.
The Türkiye-Romania-Bulgaria undersea infrastructure mission also strengthens the study's wider argument. Coastal-state cooperation is no longer confined to drifting mines. It is developing into a standing security framework for the Black Sea's cables, pipelines and other strategic assets.
The central conclusion remains strong: NATO and European governments cannot construct a Black Sea security plan around Türkiye. They must construct it with Türkiye. Ankara's preference is not to remove Russia from the regional order but to prevent either Russia or non-coastal NATO powers from dominating it.
Read the study:Managing Montreux: Turkey and the Russia-Ukraine War in the Black Sea
Sources: Carnegie Europe, Bosphorus News review and reporting.