The US Navy said it is helping the crew of two oil tankers after a "reported attack" in the Gulf of Oman, just weeks after the US accused Iran of attacking other oil vessels in the same area.
Two tankers were reportedly damaged by explosions early on Thursday morning but shipping sources said their crews were safe.
Details were scarce but Tradewinds, a shipping magazine, reported that one of the ships had been hit by a torpedo.
The UK Maritime Trade Operations (UKTMO), a unit of the Royal Navy, said it was aware of an incident in the area. "UK and its partners are currently investigating," UKTMO said.
The alleged attack came just weeks after the US accused Iran of sabotaging two oil tankers and two smaller ships near the Emirati port of Fujairah using naval mines on May 12. Iran denied responsibility for the attack.
The latest incident comes amid weeks of heightened tensions between the US and Iran.
The US has been building up forces in the Middle East since early May, when the White House said it had evidence that Iran was preparing attacks against American troops in the region.
Since then the US has sent an aircraft carrier, 1,500 additional troops, a bomber task force and several batteries of missile interceptors to the region.
Donald Trump has repeatedly said he is not looking to provoke a war with Iran but the UK and other allies fear that the two sides could stumble into an unintended conflict.
Meanwhile, Shinzo Abe, the prime minister of Japan, is visiting Iran. The trip is officially commemorating 90 years of diplomatic relations between Iran and Japan but Mr Abe has also said he is eager to try to calm tensions between the two sides.