Indonesia’s coast guard said Tuesday it has seized an Iranian-flagged tanker suspected of involvement in the illegal transshipment of crude oil.

The vessel, MT Arman 114, was carrying 272,569 metric tons, or nearly two million barrels of light crude oil and was suspected of transferring the oil to another vessel without a permit, the coast guard said in a statement. Such a large tanker is considered Very Large Crude Carrier (VLCC).

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.

Iran has been shipping its oil by illicit methods since the US imposed full third-party oil sanctions in May 2019, one year after pulling out of the 2015 JCPOA nuclear deal.

It is daily exports of more than 2 million barrels per day in 2017, dropped to less than 250,000 in 2019 and 2020.

Exports picked up again at the end of 2020, as the newly elected US President Joe Biden signaled his readiness to negotiate with Iran to restore the JCPOA.

Since then, Iran’s illicit exports, mostly to China, have reached 1.5 million barrels per day, with critics accusing the Biden administration of lax sanctions enforcement.

The common method for Iran to hide its oil exports is ship-to-ship transfers outside ports, when cargos on its tankers are pumped into other vessels, which then carry it to destination as oil from other countries, such as Oman or the United Arab Emirates with forged documentation.

Updated at 15:00 GMT