The largest ship in the Iranian navy caught fire and later sank Wednesday in the Gulf of Oman under unclear circumstances, semiofficial news agencies reported.

The Fars and Tasnim news agencies said efforts failed to save the support ship Kharg, named after the island that serves as the main oil terminal for Iran.

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The blaze began around 2:25 a.m. and firefighters tried to contain it, Fars said. The vessel sank near the Iranian port of Jask, some 1,270 kilometers (790 miles) southeast of Tehran on the Gulf of Oman near the Strait of Hormuz — the narrow mouth of the Persian Gulf.

Photos circulated on Iranian social media of sailors wearing life jackets evacuating the vessel as a fire burned behind them. State TV and semiofficial news agencies referred to the Kharg as a “training ship.” Fars published video of thick, black smoke rising from the ship early Wednesday morning.

Satellite photos from Planet Labs Inc. analyzed by The Associated Press showed the Kharg off to the west of Jask on Tuesday. Satellites from the U.S. National Oceanic and Atmospheric Administration that track fires from space detected a blaze at the site of the Jask that started just before the time of the fire reported by Fars.

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The Kharg serves as one of a few vessels in the Iranian navy capable of providing replenishment at sea for its other ships. It also can lift heavy cargo and serve as a launch point for helicopters. The ship, built in Britain and launched in 1977, entered the Iranian navy in 1984 after lengthy negotiations that followed Iran’s 1979 Islamic Revolution.

Iranian officials offered no cause for the fire aboard the Kharg. However, it comes after a series of mysterious explosions that began in 2019 targeting ships in the Gulf of Oman. The U.S. Navy later accused Iran of targeting the ships with limpet mines, timed explosives typically attached by divers to a vessel’s hull.

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Iran denied targeting the vessels, though U.S. Navy footage showed members of Iran’s Revolutionary Guard removing one unexploded limpet mine from a vessel. The incidents came amid heightened tensions between the U.S. and Iran after then-President Donald Trump unilaterally withdrew America from Tehran’s nuclear deal with world powers.

The sinking of the Kharg marks the latest naval disaster for Iran. In 2020 during an Iranian military training exercise, a missile mistakenly struck a naval vessel near the port of Jask, killing19 sailors and wounding 15. Also in 2018, an Iranian navy destroyer sank in the Caspian Sea.