Drones struck two ships off Bulgaria's Black Sea coast overnight. Five crew from the sunken ship were rescued.

11 crew members from the sunken ship remain missing. All 15 crew on the other damaged ship were rescued.

Bulgarian Prime Minister Rumen Radev said emergency rescue operations followed. He said all logic suggested Russia was responsible.

But Bulgaria had no clear proof of who carried out the strikes. Russia's role has not been confirmed.

Bulgaria condemned the attacks and summoned the Russian ambassador after the strikes. The ambassador said she had no information.

She did not rule out a provocation by a third party. Bulgaria faced a second wave of drone attacks in the past week.

The attacks targeted merchant ships off its coast. A drone attack sank another ship off Bulgaria about a week earlier.

10 crew members were lost at sea. Russia has been accused of repeatedly targeting civilian cargo ships.