Bulgarian Prime Minister Rumen Radev summoned the Russian ambassador after two merchant ships were struck by drones off Bulgaria's Black Sea coast and one of them sank, according to the BBC.

Eleven sailors from the sunken ship were missing at sea on Tuesday, according to Reuters. The other ship, the Ukrainian-owned Chelsea 3, sailing under the Maltese flag, was hit 18 nautical miles from the town of Byala, and all 15 crew were rescued, according to the BBC.