One tanker carrying methanol was damaged in the Gulf of Oman (Picture: IRIB News/DPA).
The UK is prepared to assist in any rescue effort or investigation over the "completely unacceptable" suspected attacks on two oil tankers in the Gulf of Oman, Downing Street has said.
The two civilian ships were damaged off the coast of Iran on Thursday amid heightening tensions between the US and Tehran, but many details remain unclear.
An alert urging "extreme caution" was issued by the Royal Navy-run United Kingdom Maritime Trade Operations following reports of explosions.
Sailors were forced to evacuate when one of the tankers was left ablaze and the other adrift.
Theresa May's official spokesman told a Westminster briefing: "Attacks on civilian vessels like these are completely unacceptable.
"We are in contact with international partners and are ready to assist in any rescue effort or investigation."
Video: Defence analyst Christopher Lee said it is "scary" if a torpedo was used in the suspected attack.
Iran's Islamic Republic News Agency (IRNA) claimed the Front Altair vessel had sunk, however, Norwegian shipping company Frontline dismissed those reports and said the vessel was still afloat.
Taiwan's state oil refiner CPC Corp said the Front Altair was "suspected of being hit by a torpedo".
Defence analyst Christopher Lee said: "That is scary because if you use a big weapon like that [a torpedo] then you're looking for an explosion, you're looking for destruction.
"Then you're looking at the fact that America might feel forced to do something.
"And when a country is forced to do something, it's planning is not always 100%.
"That is when you get mistakes and miscalculation, and mistakes and miscalculation is a cause of minor conflict."
Dr Aziz Alghashian, a Middle East politics expert, said he expects there to be an "increased military presence" in the region to ensure the shipping lanes remain open.
He said any military involvement would be "in the form of protection" rather than "confrontation".
American warship USS Bainbridge has been helping with the aftermath of the incident which took place 25 miles off the Iranian coast.
The group also said they were investigating the incident.
Japan's trade ministry said the two vessels had "Japan-related cargo".
Prime minister Shinzo Abe had been wrapping up a high-stakes visit in Tehran which was aimed at easing tensions between Iran and the United States.
The incident comes just a month after four oil tankers were attacked nearby, off the coast of the United Arab Emirates.
The United States accused Iran who denied being involved.
Tensions have escalated in the Middle East as Iran appears poised to break the 2015 nuclear deal with world powers.
The country is set to break the uranium stockpile limit set by Tehran's nuclear deal with world powers in the next 10 days, Iran's atomic agency said on Sunday.
Spokesman Behrouz Kamalvandi said Iran would increase uranium enrichment levels "based on the country's needs".
Mr Kamalvandi also acknowledged that Iran has already quadrupled its production of low-enriched uranium.
President Donald Trump pulled the US out of the deal last year and has accused the country of being "the number one provocateur of terror".
The US recently sent an aircraft carrier and bombers to the Persian Gulf, to counter what it says is a growing threat from Iran.