A huge oil tanker has reportedly been torpedoed in an attack off the coast of Iran.
A second tanker was said to have been targeted by a magnetic mine.
The huge vessels - identified as Front Altair and Kokuka Courageous - were evacuated, and the incident immediately prompted a surge in crude oil prices.
The Front Altair, which was carrying crude oil, was struck by a torpedo, sources told shipping industry newspaper TradeWinds.
According to Pakistani media, the tankers - said to be carrying crude oil - had sent distress signals.
The US Fifth Fleet confirmed that two tankers had been damaged in the Sea of Oman.
It comes amid heightened tension between the US and Iran following an attack on four vessels in the Emirati coast a month ago.
On May 12, four oil tankers were targeted off the coast in Fujairah - with the US accusing Iran of sabotaging the vessels in an attempt to raise oil prices.
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Shipping company Berhard Schulte, owner of the Kokuka Corageous, said: “The hull has been breached above the water line on the starboard side.
“All crew are reported safe and only one minor injury reported.”
The United Kingdom Maritime Trade Operations, which is part of the UK Royal Navy, said on
Thursday that it was aware of an incident in the Gulf of Oman, near the Iranian coast.
"The UK and its partners are currently investigating," it said.
No one is believed to have been hurt in the suspected attack.
Al Alam TV station in Iran reports that "successive explosions" took place 25 miles off the Iranian coast.
A shipping broker told Reuters the explosion may have involved a magnetic mine on the Kokuka.
The source stated: "All crew safely abandoned the vessel and was picked up by Vessel Coastal Ace.
"Kokuka Courageous is adrift without any crew on board."
Joshua Frey of the US Fifth Fleet said: "We are aware of the reported attack on tankers in the Gulf of Oman. U.S. Naval Forces in the region received two separate distress calls at 6.12am local time and a second one at 7am."
Sources identified the tankers to Reuters as the Marshal Islands-flagged Front Altair and the Panama-flagged Kokuka Courageous.
An official told Bloomerg the Front Altair is on fire, having been loaded with oil in Abu Dhabi.
The US blamed Iran for the Fujairah attack last month, with US National Security Adviser John Bolton stating: "It's clear that Iran is behind the Fujairah attack.
"Who else would you think would be doing it? Someone from Nepal?"
And State Secretary Mike Pompeo said the attack had been carried out to raise the global price of oil.
Tehran has denied claims it carried out the attack using naval mines.
According to Bloomberg, the price of Brent oil crude jumped by 4.5% in the wake of this morning's attack.
