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An abandoned tanker has sunk off Yemen's southern coast spilling out fuel into the Gulf of and along the shores of the war-torn nation, port officials said.

Mohammed Amzarba, head of Aden's port authority, told the official Saba news agency on Thursday that the authorities were warned last week that the boat, named as the Dia, was sinking.

Amzarba said port authorities had tried to use a tug to secure the Dia, but that "specialised companies" would have been needed for the job.

Another official at Aden port said the vessel had been moored since 2014 at Al-Bariqah, west of the main port, and had held stores of diesel.

It was not clear how much fuel was stored in the ship held when it sank.

Leaking fuel had now spread along the coast for some 20 kilometres (12 miles) added the second port official, who did not want to be named.

Oil was seen by AFP correspondents washing onto shores surrounding Aden.

Ahmed Fahim, a member of the environmental rescue committee in Aden, said no one had taken "care of the maintenance of the tanker, so it sank and caused a disaster on the coast."

A preliminary government report said the spill had reached a nearby nature reserve. Fahim said dead fish had "washed up on shore."

Several other boats are also abandoned at Aden, raising fears of more potential environmental disasters.

The incident has also rekindled concerns about the fate of the 45-year-old fuel vessel FSO Safer, anchored near Yemen's western Red Sea port of Hodeida since 2015, with 1.1 million barrels of crude on board.

The UN says it threatens a catastrophic oil spill that would destroy marine ecosystems, shut down the fishing industry and close Yemen's lifeline Hodeida port for six months.

Yemen has been devastated by civil war between the government -- supported by a Saudi-led military coalition -- and the Iran-backed Houthi rebels since 2014.

Tens of thousands of people, mostly civilians, have been killed and millions displaced in the conflict.