Turkey declared that the situation in Ukraine had evolved into a war, which allowed Turkey to invoke the Montreux Convention
According to the 1936 Montreux Convention, Turkey controls both the Bosporus and Dardanelles straits. It is an essential element in the context of Black Sea security and stability.
In the event of a war, the pact gives Turkey the authority to regulate naval warship transit and close the straits to warships from the countries involved in the conflict.
Russia launched a land, sea, and air assault on Ukraine in the biggest attack by one state against another in Europe since WW2. Turkey declared that the situation in Ukraine had evolved into a war. This declaration gives Turkey the authority to invoke the Montreux Convention and prohibit Russian warships from entering the Black Sea via the Bosporus and Dardanelles straits.
The straits of Bosporus and Dardanelles connect the Aegean and Black Seas via the Sea of Marmara. It is the only way for Black Sea ports to access the Mediterranean and beyond. It will allow them to restrict Russian warship movement between the Mediterranean Sea and the Black Sea.
However, Russia’s location on the Black Sea complicates matters. Article 19 of the treaty makes an exception for Black Sea countries that can effectively undermine Turkey’s power by preventing Russian warships from entering or exiting the Black Sea.