Bulgaria has launched a search-and-rescue operation after the two vessels were attacked overnight about 70 nautical miles east of Byala, with authorities yet to find survivors from the sunken ship, the Bulgarian government said on Tuesday.

“One of the ships, sailing under the flag of Togo, has sunk,” Radev said at the start of a meeting with representatives of Bulgaria’s defence, interior and transport ministries, as well as security services and other institutions.

The Bulgarian ro-ro passenger vessel DIOSCURIA, which was in the area, witnessed the explosion and moved towards the site.

Authorities found an overturned boat, three rafts and life jackets, but “at the moment there is no information about survivors”, the government said.

The second commercial vessel was damaged in the attack and a fire broke out on board. Its crew was evacuated, with two injured sailors taken to Varna aboard a Bulgarian Navy vessel for medical treatment.

The remaining crew members were being brought ashore by a Bulgarian border patrol boat.

The government said Turkish and Indian citizens were among them.

The Maritime Rescue Coordination Centre in Varna is leading the operation, with the Navy, Air Force, Border Police and maritime administration involved.

Two helicopters from Bulgaria’s 24th Air Base were placed on standby to conduct flights over the area if required. A Su-25 aircraft was also tasked with reconnaissance to search for survivors from the crews of the two vessels.

Radev called the attack “absolutely unacceptable” and said it represented a serious breach of international law and maritime practice.

“For us, as a state that bears responsibility in its exclusive economic zone, the most important thing is the health and lives of people, regardless of who is sailing in this zone,” he said. “We are obliged to conduct emergency rescue operations for search and rescue.”

The prime minister also warned about the wider implications for Black Sea shipping.

“This latest incident creates additional risks for shipping in the Black Sea and leads to a further increase in costs and insurance risks for maritime transport,” Radev said.

He added: “If this war is not ended in time, it will continue to expand its geographical scope and increase the risk even of global conflict. We are seeing civilian vessels being attacked.”

Bulgarian authorities are also monitoring another damaged vessel drifting in the Black Sea without a crew after its steering system failed.

Government institutions have been placed on standby to intervene if necessary to prevent any threat to Bulgaria’s coastline.

The government said authorities were also monitoring the area for possible marine pollution from the damaged vessels, while the search for the crew of the sunken ship was continuing.

The identities of those responsible for the attacks were not stated in the Bulgarian government’s latest account.