Defence minister Dimitar Stoyanov says a Su-25 jet will fly over Bulgaria's economic zone in the Black Sea to search for survivors after drones hit two cargo ships.

"We're getting a Su-25 ready for aerial reconnaissance," Stoyanov said. He explained the jet can fly over the sea at lower speed, which makes it easier to spot people in the water.

The minister spoke after a meeting with officials called by prime minister Rumen Radev.