Indonesia’s coast guard said today that it seized an Iranian-flagged supertanker suspected of involvement in the illegal transshipment of crude oil, and vowed to toughen maritime patrols.

The MT Arman 114 was carrying 2,72,569 metric tons of light crude oil, valued at 304 million dollars. The vessel was captured on Friday after being spotted in Indonesia’s North Natuna Sea, carrying out a ship-to-ship oil transfer with the Cameroon-flagged MT S Tinos.

Along with the MT Arman, authorities detained its captain, 28 crew, and 3 passengers, who were the family of a security officer on board.