IRAN's largest navy ship caught fire after a mysterious blast in the "engine room" and burned for 20 hours in the Gulf of Oman before sinking.
The blaze broke out onboard the British-built Kharg during a training mission at around 2.25am today.
It's reported the vessel sank near the port of Jask on the Gulf of Oman.
"All efforts to save the vessel were unsuccessful and it sank," Iran's Fars news agency reported.
The entire crew managed to evacuate the ship and pictures shared on Iranian social media showed images of sailors wearing life jackets as they fled the vessel.
The ship was on fire for 20 hours as military officials battled to extinguish the flames before it finally went down.
Tehran-based defence and security expert Hossein Dalirian said "speculations about attacks on the ship are not true".
"This happened due to a technical defect in the engine room," he .
Iranian state media also suggested an electrical fire may have broken out shortly after 2am.
The military has not confirmed the cause of the blaze.
The fire occurred in the Gulf of Oman - a waterway that is connected to the Strait of Hormuz where around a fifth of the world's oil passes through.
The Kharg was built in Britain in 1977 and entered the Iranian navy in 1984 following the 1979 Islamic Revolution.
Named after the Iranian island that is the site of its main oil refinery, the ship can lift heavy cargo and acts as a launch pad for helicopters.
Relations between the UK and Iran soon soured after the revolution when arms exports to Iran from Britain ceased, prompting a standoff over a £400million order for tanks.
UK officials recently played down the prospect of Nazanin Zaghari-Ratcliffe's imminent release from Iran after it was suggested Boris Johnson's government had agreed to pay the debt over the non-delivery of tanks dating back to the 1970s.
UK government sources stressed the reports from Iran's state broadcaster were "wrong" and insisted that nothing had been paid and they were not expecting the reported debt to be settled.
Nazanin was arrested in Tehran in 2016 as she was returning to Britain.
The charity worker was released from a five-year jail term in April after being accused of spying.
But she was caged for another year on charges of propaganda activities against the regime.
US security officials are also monitoring two Iranian warships that could be heading for Venezuela after a frigate, known as the Makran, was pictured sailing along the east coast of Africa.
They are trying to determine the destination of the journey, the motives behind it and what cargo the vessel could be holding.
Intelligence officials believe it is heading to Venezuela, anonymous sources told
Tensions are increasing between the US and Iran and it's thought it could be an intimidation tactic towards Washington from president Hassan Rouhani.
Iran and Venezuela are under heavy sanctions from the US and have formed a close relationship.
The blaze comes just a week after a major explosion occurred at a drone factory in Iran, injuring nine.
The reason behind the blast remains unknown but it happened just days after Israel accused Tehran of providing support to Hamas during the recent conflict in Gaza.
Benjamin Netanyahu accused Iran of arming Hamas militants by helping develop deadly missiles to strike strategic targets in Israel.
The weapons were thought to be manufactured in Gaza based on an Iranian design.
Hamas has previously relied on short-range Qassam rockets which have a range of around six miles.
But rockets with a range of 25 miles, as well as the M-75 and J-80 rockets, that have a longer range of up to 60 miles have also been used in the conflict.
Senior officers within Hamas made regular visits to Iran to undergo training in the production and operation of sophisticated weaponry, according to reports.
Last month, a US vessel fired around 30 warning shots to fend off Iranian speedboats that were reportedly “harassing” a ballistic missile sub in the Strait of Hormuz.
Around thirteen Iranian speedboats “conducted unsafe and unprofessional” manoeuvres near it, according to the Pentagon.
Pentagon spokesman John Kirby said the speedboats from Islamic Revolutionary Guard Corps Navy (IRGCN) came as close as 150 yards to six U.S. military vessels.
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The sinking of the Kharg is the latest naval disaster for Iran.
Last year, 19 sailors were killed after a missile accidentally struck a vessel near the port of Jask. At least 15 crew members were injured.