The Turkish Foreign Ministry has signaled that it intends to prevent Russian warships from passing through the Bosphorus and Dardanelles straits that lead to the Black Sea, a change in Turkey’s once neutral position where officials pointed to alliances with Russia and Ukraine.

“We have come to the conclusion that the situation in Ukraine has turned into a war,” Turkish Foreign Minister Mevlüt Çavuşoğlu said. “We will apply the Montreux provisions transparently.”

Turkey controls the two straits under the Montreux Convention, granting it the power to block the passage of Russian and Ukrainian warships, provided they do not return to their permanent bases in the Black Sea.

The convention means that the strait can be blocked if a conflict meets the definition of a war.

The blockage will likely affect a number of Russian ships currently in the Mediterranean Sea, including submarines and frigates, some of which belong to Black Sea fleets. A block means that Russian warships will not be able to transit through the strait to provide reinforcements to existing forces or to depart and return to assist forces in their invasion of Ukraine.

Turkish maritime analyst Yörük Isik referred to satellite images showing at least 16 ships in the Mediterranean. “What we see are 16 ships, some of which are Black Sea Fleet ships. They might have additional assets, including supply tankers or small patrol craft near Tartus, but those are most significant strengths,” he said.

Çavuşoğlu’s remarks on closing the strait also signaled a change in Turkish policy which, until now, has carefully tried to balance its commitments to NATO and its alliance with Ukraine alongside its energy dependence and security vis-à-vis Russia.

Turkey’s position evolved rapidly over the weekend, including Remarks earlier today by President Erdogan’s chief adviser, Ibrahim Kalin, who said “we will continue our efforts to help the people of Ukraine and end the bloodshed in this unjust and illegal war.” So far, Turkish officials have chosen their words carefully, mostly using terms such as “military operation”.

Turkey’s decision to close the strait is a signal that its current foreign policy prioritizes Europe and its commitments to NATO over its long-term ties with Russia.

“Turkey is dependent on Russia, not only in terms of energy like some European countries, but also in terms of their security situation. There must be fears within the authority that Russia is giving the green light to an attack by [Syrian] regime on Idlib,” said Sinan Ülgen, of the Turkish think tank Center for Economic Studies and Foreign Policy. He was referring to the northern Syrian province controlled by opposition forces, including jihadists, with a Turkish presence to deter Russian and Syrian attacks.