Greece has advised Greek-flagged commercial ships to upgrade security measures when sailing in the Black Sea following a string of attacks on tankers over ‌the past days, according to a shipping ministry advisory seen by Reuters.

Greek-operated ships are among the world’s largest fleets of tankers and are pivotal for trade across the Black Sea region, whose waters are shared by Bulgaria, Georgia, Romania and Turkey, ⁠as well as warring Russia and Ukraine, which Moscow invaded in February 2022.

In recent weeks, Ukraine and Russia have stepped up attacks on vessels and other facilities in the Black Sea and the Sea of Azov, trying to undermine each other’s war efforts.

On Sunday, a Russian missile struck a ship carrying corn near Ukraine’s southern port of Odesa, killing 10 people.

Two Greek-operated tankers were also attacked ‌with ⁠sea drones on Sunday at the Caspian Pipeline Consortium – a 1,510 km oil pipeline connecting Kazakhstan’s Caspian Sea oil fields with Russia’s Black Sea port of Novorossiysk. CPC accounts for about 80% of Kazakhstan’s oil ⁠exports.