An Iranian vessel sank in the Gulf of Oman on Wednesday after unsuccessful efforts to put out a fire, the navy said, adding that the crew was able to disembark with no loss of life.

How Iranian media say events unfolded

Iranian state television said the fire broke out on the "Kharg," Iran's highest-tonnage naval vessel, at around 2:25 a.m.on Wednesday (21:55 UTC) near the Iranian port of Jask.

The ship was on a training mission some 1,270 kilometers (790 miles) southeast of Tehran on the Gulf of Oman.

Firefighting efforts continued "for 20 hours" before the ship went down, Iran's navy said.

"All efforts to save the vessel were unsuccessful and it sank," the semi-official Fars news agency reported.

How did the fire start?

The cause of the fire, which according to a navy broke out in "one of the systems" of the vessel, was not immediately known.

Photos of the fire on social media showed Iranian sailors evacuating on speedboats as huge plumes of smoke were seen rising from the vessel behind them.

Iran's largest naval ship

Kharg, named after the island that serves as the main oil terminal for Iran, was the country's largest navy ship.

It served as one of a few vessels in the Iranian navy capable of providing replenishment of supplies — most notably refueling — to other vessels at sea.

Kharg could also lift heavy cargo and served as a launch point for helicopters. The ship was built in the United Kingdom and launched in 1977. It entered the Iranian navy in 1984 after lengthy negotiations following the 1979 Islamic Revolution.

kmm,adi/msh (AFP, AP)