ANKARA— Turkey has been caught off guard as its strategic partner Russia invaded its other strategic partner, Ukraine.

Russia is Turkey’s biggest energy supplier. Russia and Ukraine together are Turkey’s biggest tourist markets and grain suppliers. Turkey faced suspension from the U.S.-led, multinational program that builds the F-35 Lightening II as it insisted on becoming the first NATO ally to deploy on its soil the Russian-made S-400 long-range, air-defense system. Turkey supplies armed drones to Ukraine.

Turkey says it supports Ukraine’s territorial integrity and calls the Russian invasion “unacceptable.” Yet Turkey also abstained on Feb. 25 from voting on suspending Russia’s membership in most bodies of the Council of Europe.

But there had to be a limit to this act of delicate balancing: The pair of straits connecting the Mediterranean Sea to the Black Sea, a maritime chokepoint of immense importance.

Ukraine asked Turkey to block the passage of Russian military vessels from the Dardanelles and Bosphorus straits. At least six Russian warships and a submarine transited Turkey’s straits in February.

But that is a matter concerning the articles of the 1936 Montreux Convention that permits Turkey to limit naval transit of its straits during wartime, or if threatened. Is this, technically and legally, a war?

In a rhetorical shift, Turkey on Feb. 28 called Russia’s assault on Ukraine a “war.” That paved the way for the Ankara government to implement parts of the Montreux Convention, potentially limiting the transit of Russian warships from the Mediterranean to the Black Sea.

“It is not a couple of air strikes now, the situation in Ukraine is officially a war… We will implement the Montreux Convention,” Mevlut Cavusoglu, Turkey’s foreign minister, said on February 27.

Cavusoglu reiterated that Turkey cannot block all Russian warships accessing the Black Sea due to a clause in the pact exempting those returning to their registered base. “There should not be any abuse of this exemption. Ships that declare returning to their bases and passing through the straits should not be involved in the war,” Cavusoglu said.

But on Feb. 28 Cavusoglu warned all Black Sea littoral or non-littoral countries against transiting naval vessels through the Turkish straits.

He said, citing the Montreux Convention, that “In the event of war to which Turkey is not a party, Turkey has the right to block naval shipping traffic through the straits.”

On March 1, Cavusoglu told Haber Turk TV that Moscow on Feb. 27 and 28 requested transit passage rights for four naval vessels. Three of the vessels were registered at Russia’s Black Sea ports and one was not.

“Through dialogue with our Russian partners we advised against the transit for all four ships,” the minister said. “The Russians agreed.”

Editor’s note: This story was updated on March 2 to include a March 1 statement by the Turkish foreign minister.

Burak Ege Bekdil was the Turkey correspondent for Defense News.

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