Five armed Iranian Revolutionary Guard boats unsuccessfully attempted to seize a British oil tanker in the Gulf, according to US officials.
The tanker was entering the Strait of Hormuz, a strategic shipping route between Iran and the Arabian Peninsula, when it was approached by the Iranian vessels, according to the official, cited on CNN and Fox News.
The Iranians ordered the tanker to stop in Iranian territorial waters, but a British naval vessel escorting the tanker aimed its guns at the Iranian boats and warned them to move away, which they did, the reports said.
The incident was said to be filmed by a US aircraft overhead.
There's been no immediate comment from either Britain or Iran on the claims.
Britain last week impounded an Iranian oil tanker in Gibraltar, on the southern tip of Spain, on suspicion of violating EU sanctions against Syria.
The move sparked a diplomatic row between Britain and Iran, with Tehran summoning the British ambassador.
Earlier on Wednesday, Iranian President Hassan Rouhani said Britain would face "consequences" over the seizure of the Iranian tanker.
Washington has accused Tehran of being behind a series of recent attacks against commercial vessels near the Strait of Hormuz.
Last month, President Donald Trump came close to ordering an airstrike in retaliation against Iran for shooting down a US spy drone near the Strait.
General Joseph Dunford, chairman of the US military's Joint Chiefs of Staff, said Tuesday the US was attempting to build a military coalition to protect shipping in the region.
"We are engaging now with a number of countries to see if we can put together a coalition that would ensure freedom of navigation both in the Straits of Hormuz and the Bab el Mandab," Dunford said.