Drone strikes hit two commercial vessels in Bulgaria’s Black Sea exclusive economic zone on Tuesday, sinking one ship and leaving its crew missing.

The Togo-flagged Alfa Watan and the Palau-flagged Able were attacked by sea and aerial drones around 3 am off Byala, about 80 nautical miles from the coast. The Alfa Watan sank, while the Able caught fire and was abandoned.

The 18 crew members of the Able, including 11 Turkish and seven Indian nationals, were rescued by a passing ferry, with two injured. The crew of the Alfa Watan remains missing and a search is underway.

Bulgarian Prime Minister Rumen Radev called the attack a gross violation of international law. EU Commission President Ursula von der Leyen said attacks on civilian shipping are unacceptable. The origin of the drones has not been established.

A maritime source said the strike was probably Russian, though Moscow did not comment. It appears to be the first such attack in Bulgarian waters. Two ships were hit in the attack, Radev said.