However, the company's statement contradicted earlier claims that the damage to the M. Star on Wednesday had occured after it was hit by a freak wave.

A coast guard official in Oman, in whose territorial waters the incident took place, told the Reuters news agency that "the boat was hit by a tremor ... we have no information of an attack".

'Mystery and intrigue'

Dan Nolan, Al Jazeera's correspondent in the UAE, said that details of the incident were unclear.

"It is certainly shrouded in mystery and intrigue ... a port official here in the UAE was questioned about what may have caused this, he was quite vague about what it could be," Nolan said.

"We know that pirates will try to stop vessels by two means: rocket propelled grenades or ramming the boat"

Will Geddes,
security specialist 

"When asked if it was possible it could be a sea mine, he said that yes, it is possible. It was a collision of some sort and anything is possible, it could be a submarine, it could be anything." 

The damage to the vessel's hull is being examined by experts off Fujairah, one of the UAE's emirates, and the incident is under investiation.

The ship's owners from Japan have hired a Dubai-based specialist in military attacks to head [to the port] to also cast an eye over this," Nolan said.

Will Geddes, a London-based security specialist, told Al Jazeera that pirates could have been behind the alleged attack.

"We know that pirates will try and stop vessels by two means: rocket propelled grenades or ramming the boat," he said.

Geddes said it seemed unlikely that the tanker had hit a mine as that would have probably breached the tanker's hull.   

The M. Star had been filled with sabout 2.3 million barrels of crude oil on Tuesday at the UAE port of Das Island and was heading for Chiba port in Japan.

Around 17 million barrels of oil are transported through the Straits of Hormuz every day.

Al-Qaeda has previously threatened to carry out attacks in the key transit route for much of the world's supply of crude.