Bulgarian investigators will examine debris found near the Chelsea-3, a ship hit by drones in the Black Sea. Transport minister Georgi Peev told reporters in the village of Kaloyanovo, near Plovdiv.

The strikes on two merchant ships in Bulgaria's economic zone came to light in early October. Democratic Bulgaria then asked for an emergency hearing in parliament, and president Iotova cancelled a visit to Tarnovo. On 13 October, prime minister Rumen Radev said more ships had been attacked in the Black Sea off Bulgaria.

The previous development: Democratic Bulgaria calls for emergency hearing after strike on ships

Chelsea-3 is a motor ship sailing under the Maltese flag. The Transport Ministry organised an operation to tow it to shore on Saturday, and it now lies in the port of Burgas with three large holes in its hull. It was hit 17 nautical miles east of Byala. All 15 crew members were rescued.

A drone also hit HS Dignity, which sails under the flag of Guinea-Bissau. It was 17 nautical miles east of Shabla when the ship sank.

Peev does not know what the debris is or where it was found. "I have no information. It is very important that every institution and ministry knows its own duties," he said. He explained that his ministry manages ship traffic in the 12-mile zone and runs search and rescue operations.

Bulgarian services are already investigating. If they lack the technical means, they will bring in partner organisations with experience in such cases. "We have taken the ship in because we want an impartial investigation," Peev said.

The minister called the cost of the towing a legal and financial matter that comes down to details. The ship is insured, he said, and the issue will be discussed and journalists will be told.

The Military District Prosecutor's Office in Sofia opened pre-trial proceedings yesterday after a report of an alleged crime linked to Chelsea-3. Prosecutors say it took place in Bulgaria's exclusive economic zone in the Black Sea.