US investigators believe Iran or groups it supports used explosives to damage four ships off the United Arab Emirates (UAE) on Sunday, media reports say.
Military experts were reportedly sent to investigate the incident and found a large hole in each of the tankers.
No evidence has emerged to show that Iran was involved. The affected countries are yet to assign blame.
The incident has increased tensions between Iran, which borders the nearby Strait of Hormuz, and the US.
About a fifth of oil that is consumed globally passes through the strait. Last month, Iran threatened to close it if it was prevented from using the waterway.
This followed a US decision to end exemptions from sanctions for major importers of Iranian oil.
The team of US military investigators discovered large holes in all four of the affected ships and believe they were caused by explosive charges, the Associated Press reports, quoting an unnamed official. They did not explain how the damage was linked to Iran.
CBS carried a similar report quoting unnamed US officials.
Few details have been released about the incident, which is said to have taken place at about 06:00 (02:00 GMT) on Sunday within UAE territorial waters in the Gulf of Oman, east of the emirate of Fujairah.
The UAE foreign ministry said four commercial ships had been targeted in a “sabotage attack” near Fujairah port, just outside the Strait of Hormuz.
There were no casualties but Saudi Arabia said two of its ships had suffered “significant damage”.
The Saudi energy minister, Khalid al-Falih, said one of the tankers had been on its way to be loaded with Saudi oil which was to be delivered to customers in the US.
Another damaged tanker was Norwegian-registered, while the fourth was reportedly UAE-flagged.
Saudi TV has shown images of the damaged Saudi ships, and a picture released by the UAE shows a Norwegian-flagged vessel, Andrea Victory, with damage to its hull.
Thome Ship Management, a Norwegian firm which manages the ship, said in a statement it had been “struck by an unknown object on the waterline”.
Compared with previous attacks on shipping in the Middle East – the USS Cole in 2000, the Limburg tanker in 2002 and more recent attacks off Yemen – the damage done to four tankers off the UAE coast on Sunday is minimal. –BBC