Turkey has restricted the entry of commercial ships into the Black Sea. Bloomberg, citing informed sources, reported that the measure was taken after increased concern by the Turkish government as Russia’s and Ukraine’s attacks on vessels in the region intensified.

Based on the report, Turkey’s Directorate General of Coastal Safety has told several ships heading to the Russian port of Novorossiysk that it is currently not issuing transit permits through the Dardanelles for such trips or needs more time to review applications. Novorossiysk is the main hub for Russian oil and grain exports.

Turkish officials have not offered an explanation for the decision. Sources said some vessels have learned that the restriction also applies to ships bound for Ukraine.

Earlier this week, Turkey’s Ministry of Foreign Affairs said that a number of crew members, including Turkish citizens, were injured in drone attacks on two vessels with Turkish ownership.