Turkey activated the Montreux Convention in response to Russia's War over Ukraine.
The declaration that the situation in Ukraine had become a war, authorizes Turkey to activate the Montreux Convention and ban Russian war vessels from entering the Black Sea through the Bosporus and Dardanelles straits.
Montreux Convention is an international agreement that was signed by Australia, Bulgaria, France, Greece, Japan, Romania, Yugoslavia, the United Kingdom, the Soviet Union, and Turkey.