Indonesia's coast guard said on Tuesday 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 272,569 metric tons of light crude oil, valued at 4.6 trillion rupiah ($304 million), when it was seized last week, the Indonesian authorities said.
The Very Large Crude Carrier (VLCC) was suspected of transferring oil to another vessel without a permit on Friday, the Southeast Asian nation's maritime security agency said.
The vessel was captured after being spotted in Indonesia's North Natuna Sea, carrying out a ship-to-ship oil transfer with the Cameroon-flagged MT S Tinos, the agency's chief, Aan Kurnia, said.
"MT Arman was spoofing their automatic identification system (AIS) to show its position was in the Red Sea but in reality it is here," Aan told reporters.
"So it seems like they already had a malicious intent," Aan said, adding that the vessel also dumped oil into the ocean, in violation of Indonesia's environmental law.
The vessels' operators could not be immediately reached for comment.
Along with the Arman, authorities detained its Egyptian captain, 28 crew and 3 passengers, who were the family of a security officer on board, the agency said.
After the two supertankers attempted to escape, authorities focused their pursuit on Arman, assisted by Malaysian authorities as the vessel sailed into their waters, Aan said.
The Tinos was supposed to have been scrapped in 2018, he added. It was built in 1999 while the Arman was built in 1997, according to shipping database Equasis.
'Shadow' fleet of oil tankers from sanctioned countries transited Singapore Strait
A "shadow" fleet of tankers carrying oil from sanctioned Iran, Russia and Venezuela has been transferring cargoes in the Singapore Strait to avoid detection, a Reuters analysis showed this year.
The risk of oil spills and accidents is growing as hundreds of extra ships, some without insurance cover, have joined the opaque parallel trade over the past few years.
Aan vowed that Indonesia's coast guard, assisted by other authorities, would strengthen patrols in its waters. Indonesia is the world's largest archipelago, with about 17,000 islands.
"We have to be firm, tough," he said. "There has to be a deterrent effect so it will not happen again."
In 2021, Indonesia seized Iranian- and Panamanian-flagged vessels over similar accusations. The captains of the two vessels received two-year probation from an Indonesian court.