Sofia, Bulgaria: Two ships were struck off the Bulgarian coast on Tuesday, Prime Minister Rumen Radev said, adding that he would summon the Russian ambassador over the latest such incident in the Black Sea.
Radev wrote on social media that a Ukrainian-owned cargo ship was "hit by three aerial drones", and shortly afterwards another ship was hit and sank.
"We lack solid, clear evidence to level accusations against any specific party; however... logic suggests the outcome works to the advantage of the Russian Federation," he wrote.
Radev identified the first vessel as the Malta-flagged cargo ship Chelsea 3 and said all 15 crew members -- seven Ukrainians and eight Azerbaijanis -- had been rescued.
He said a second vessel was "struck" and one crew member had been rescued, but he gave no further details of the incident.
"This latest attack on commercial vessels in the immediate vicinity of Bulgarian territorial waters is absolutely unacceptable," Radev said.
Bulgaria will summon the Russian ambassador over the attacks, he said, and would also discuss them with NATO chief Mark Rutte.
EU chief Ursula von der Leyen condemned the attacks, calling them "another front of escalation of the Russian war in Ukraine".
"We stand with Bulgaria and thank its rescuers for their swift response. Those responsible should be held accountable," she posted on social media.
