The Liberian-flagged container ship Kontship Jet sank around midnight overnight, the Varna regional administration said. The military district prosecutor's office in Sofia has opened a pre-trial investigation into the sea drone attack on the vessel.

Three drones hit the ship around noon yesterday, about 21 nautical miles south-east of Shabla, inside Bulgaria's exclusive economic zone. All 18 crew members were rescued.

How it all started: No visible pollution found in Black Sea in first check after strike on container ship

The sailors are in Varna. The Varna regional military police service reported the case to prosecutors and is to question the crew on the spot straight away. Prosecutors say the questioning is urgent because of the emergency, and because the survivors are foreign nationals staying in Bulgaria temporarily.

The order was issued today. Given the scale and nature of the case, a military investigator from the same prosecutor's office will lead the inquiry.

The case was opened under Article 415, paragraph 1 of the Criminal Code, which covers breaking the rules of international law on waging war. The order dates the act to October 2026. It says paragraphs 67, 41 and 42 of the San Remo Manual on International Law Applicable to Armed Conflicts at Sea were breached.

Prosecutors believe someone ordered the use of banned methods of warfare: drones attacked a ship flying the flag of neutral Liberia, with its crew and cargo on board.

Investigators still have to establish who owns the ship, what it was carrying, who made up the crew, what route it was taking and how large the damage is.