Turkey on Monday activated powers under an international treaty that allows it to effectively block Russian warships from crossing the Bosphorus.

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The move comes one day after Turkish foreign minister Mevlut Cavusoglu formally labelled the Ukraine conflict as a war.

That opened the way for the government in Ankara to invoke article 19 of the 1936 Montreux Convention Regarding the Regime of the Straits, the international treaty that governs ship traffic through the Turkish Straits and allows Turkey to restrict moves of belligerent war vessels.