Dozens of crew members have been rescued after abandoning two commercial oil tankers hit by explosions in the Gulf of Oman.
Iran said it had rescued the 21 crew members on board the Japanese-owned Kokuka Courageous and the 23 on the Front Altair, owned by Norway.
The US disputed this, saying its Navy had rescued some of those aboard.
It is unclear what caused the blasts. They come amid heightened tensions between Iran and the US.
A senior Iranian official told the BBC: “Iran has no connection with the incident.”
“Somebody is trying to destabilise relations between Iran and the international community,” the official added.
The incident in one of the world’s busiest oil routes comes a month after four oil tankers were attacked off the United Arab Emirates.
No group or country has claimed responsibility for that incident, which also caused no casualties.
The US at the time blamed Iran – but Tehran denied the accusations.
President Donald Trump tightened America’s sanctions on Iran in May, and the US recently strengthened its forces in the area – saying there was a danger of Iranian attacks.
On Thursday, Iran’s supreme leader Ayatollah Khamenei ruled out any negotiations with the US aimed at easing the tensions.
He was quoted as saying during talks with Japanese Prime Minister Shinzo Abe that he did not see President Trump as being worthy of any exchange of messages.
Oil prices jumped as much as 4% after Thursday’s incident.
What do we know about the explosions?
The cause has not been confirmed.
The Front Altair had been “attacked”, the Norwegian Maritime Authority said, leading to three explosions on board.
Wu I-fang, a spokesman for Taiwan’s CPC Corp oil refiner, which chartered the Front Altair, said it was carrying 75,000 tonnes of naphtha and was “suspected of being hit by a torpedo”, although this has not been confirmed.
Other unverified reports suggested a mine attack.
The ship’s owner, Frontline, said the vessel was on fire – but denied reports in Iran media it had sunk.
The operator of the Kokuka Courageous, BSM Ship Management, said its crew abandoned ship and were rescued by a passing vessel.
The tanker was carrying methanol and was not in danger of sinking, a spokesman said.
It is currently located about 130km (80 miles) from Fujairah in the UAE and 16 miles from Iran. The cargo remains intact.
This is the second serious incident in a month involving tanker shipping close to the strategic Strait of Hormuz, through which at least one-fifth of the world’s oil passes.
In May, four tankers were hit by explosive devices close to a port in the UAE. A report presented jointly by the UAE, Saudi Arabia and Norway last week to the UN Security Council concluded they had been placed there by frogmen, but did not assign blame to any country.
But in that incident the damage was minor, there were no fires and no-one was evacuated. This is far more serious.
Both of the stricken Norwegian- and Japanese-owned tankers on Thursday were moving out of the Gulf of Oman, prompting questions as to what could have caused so much damage that the crew needed evacuating.
Iran has said it is suspicious this incident took place just as it was hosting Japan’s Prime Minister Shinzo Abe.
Who came to the rescue?
Iranian state media said Iran had rescued the crew members and they had been taken to the port of Jask.
The US 5th Fleet, based in Bahrain, said it had sent the USS Bainbridge to assist.
Spokesman Josh Frey said in a statement: “US naval forces in the region received two separate distress calls at 06:12 local time (03:12 GMT) and a second one at 07:00.”
CNN quoted a defence official as saying some mariners were transferred from a tug to the Bainbridge and then taken to Oman.
Why is this so sensitive?
The Gulf of Oman lies at one end of the strategic Strait of Hormuz, and this incident will further increase tension in a vital shipping lane through which hundreds of millions of dollars of oil pass.
The US sent an aircraft carrier strike group and B-52 bombers to the region at the start of May in response to what it said was an unspecified plan by Iran-backed forces to attack US forces in the area.
President Trump has taken a hard line towards Iran, accusing it of being a destabilising force in the Middle East.
Iran rejected the claims and has accused the US of aggressive behaviour.
Those tensions rose markedly after the 12 May limpet mine attacks in the UAE.
The UAE blamed an unnamed “state actor”. The US said that actor was Iran, an accusation Tehran has denied.
The EU called for “maximum restraint” following Thursday’s incident.
Paolo d’Amico, chairman of the tanker association, Intertanko, said the two vessels had been attacked, and expressed concern about dangers to other crews.
“If the waters are becoming unsafe, the [oil] supply to the entire Western world could be at risk,” he said.
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