TEHRAN, Jun 3 (AP) - The largest warship in the Iranian navy caught fire and later sank on Wednesday (Jun 2) in the Gulf of Oman under unclear circumstances, the latest calamity to strike one of the country’s vessels in recent years amid tensions with the West.

The blaze began around 2.25am and firefighters tried to contain it, the Fars news agency reported, but their efforts failed to save the 207-metre Kharg, which was used to resupply other ships in the fleet at sea and conduct training exercises. State media reported 400 sailors and trainee cadets on board fled the vessel, with 33 suffering injuries.

The ship sank near the Iranian port of Jask, some 1,270 kilometres southeast of Tehran on the Gulf of Oman near the Strait of Hormuz - the narrow mouth of the Persian Gulf. Satellite photos from Planet Labs analysed by The Associated Press showed the Kharg off Jask with no sign of a fire as late as 11am on Tuesday.

Photos circulated on Iranian social media showed sailors wearing life jackets evacuating the vessel as a fire burned behind them. Fars published video of thick, black smoke rising from the ship early Wednesday morning.

Satellites from the US National Oceanic and Atmospheric Administration that track fires from space detected a blaze near Jask that started just before the time of the fire reported by Fars.

Iranian officials offered no cause for the fire aboard the Kharg, though they said an investigation had begun.

Meanwhile, a massive fire broke out Wednesday night at the oil refinery serving Iran’s capital, sending thick plumes of black smoke over Tehran. It wasn’t immediately clear if there were injuries or what caused the blaze at the Tondgooyan Petrochemical Co, though temperatures in the capital reached nearly 40 degrees Celsius and hot summer weather in Iran has caused fires in the past.

The fire on Wednesday aboard the Kharg warship follows a series of mysterious explosions that began in 2019 targeting commercial ships in the Gulf of Oman. The US Navy accused Iran of targeting the ships with limpet mines, timed explosives typically attached by divers to a vessel’s hull.

Iran denied that, though US Navy footage showed Revolutionary Guard members removing one unexploded limpet mine from a ship. The attacks came amid heightened tensions between the US and Iran after then-President Donald Trump unilaterally withdrew America from Tehran’s nuclear deal with world powers. Negotiations on saving the accord continue in Vienna.

In April, an Iranian ship called the MV Saviz believed to be a Guard base and anchored for years in the Red Sea off Yemen was targeted in an attack suspected to have been carried out by Israel. It escalated a years long shadow war in the Mideast between the two countries, ranging from strikes in Syria, assaults on ships and attacks on Iran's nuclear program.

Like much of Iran's major military hardware, the Kharg dated back to before Iran's 1979 Islamic Revolution. The warship, built in Britain and launched in 1977, entered the Iranian navy in 1984 after lengthy negotiations. That ageing military equipment has seen fatal accidents as recently as Tuesday, when a malfunction in the ejector seats of an Iranian F-5 dating back to before the revolution killed two pilots while the aircraft was parked in a hangar.

The Kharg also was seaworthy enough to sail through the Suez Canal into the Mediterranean Sea and into South Asia in the past and could lift heavy cargo.

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 Jask, killing 19 sailors and wounding 15. Also in 2018, an Iranian navy destroyer sank in the Caspian Sea.