Indonesian authorities said on Wednesday that they have seized an Iranian tanker and arrested its crew members for illegally transferring oil to another vessel in the country’s exclusive economic zone.

The Iranian-flagged MT Arman 114, transporting 272,569 metric tons (2.3 million barrels) of crude oil worth 4.6 trillion rupiah (£235 million), was seized on Friday while carrying out an illegal transshipment to the Cameroon-flagged MT S Tinos near Indonesia’s Natuna waters, said coast guard chief Aan Kurnia.

An Indonesian Coast Guard vessel detected suspicious activity at dawn and tried to approach the two tankers.

The Iranian tanker fled towards Malaysian territorial waters, spilling oil as the hose connecting the two vessels came loose.

The ship ignored various signals to stop, ranging from horns and warnings via loudspeakers to shots in the air, Mr Kurnia said.

He added that the Iranian tanker, which was also carrying three passengers as well as its crew, was later arrested by the Indonesian Coast Guard with the help of its Malaysian counterpart.

The Cameroon-flagged tanker managed to escape.

Authorities are still questioning the tanker’s Egyptian captain and 28 Syrian crew members, Mr Kurnia said.

He added that they are accused of a variety of violations, including not displaying a national flag, shutting off their identification systems, anchoring illegally, as well as the illegal transfer of fuel between ships, and spilling oil.

Authorities are escorting the Iranian tanker to Batam island, near Singapore, for further investigation, Mr Kurnia said.

In 2021, Indonesian authorities seized another Iranian tanker and a Panamanian tanker over a similar illegal transfer of oil.

The tankers were released months later after a court case in which they were fined two billion rupiah (around £102,200) for spilling oil into the sea. The captains of the vessels were sentenced to one year in jail.

Iran, home to major oil and natural gas reserves, has seen its sales abroad deeply affected by US sanctions after former president Donald Trump unilaterally withdrew America from Tehran’s nuclear deal with world powers in 2018. That cut a crucial source of government revenue in Iran’s struggling economy.

Since then, Iran has relied on black-market sales and deals with Venezuela to keep its sales going.

Iran’s state-owned fleet of oil tankers routinely turn off their automatic identification systems (AIS) to try to mask where they deliver their cargo.

The AIS beacons, a safety measure so other ships know what is around them, can be tracked.

Analysts say those ships often transfer their oil to other vessels, which then sell the crude oil under false pretences.