A merchant ship has sunk and its crew is missing after a drone attack in the Black Sea, Bulgarian officials say.

A second vessel carrying grain was hit within Bulgaria's exclusive economic zone, Prime Minister Rumen Radev said. Its crew of 18 were rescued. The attacks took place at about 03:00 (23:00 GMT), some 70 miles (112 km) off the coastal town of Byala in eastern Bulgaria, and involved air and sea drones, Radev said. The sunken ship was flying the flag of Togo.