The Pentagon said the incident was serious. It described the Iranian actions as “careless, reckless and potentially hostile” and said Tehran should provide an explanation.

The Iranian Foreign Ministry described the incident as ordinary.

“The example that happened on Saturday was similar to previous cases and is an ordinary and natural issue,” Foreign Ministry spokesman Mohammad Ali Hosseini told Iran’s official IRNA news agency.

The incident is the latest sign of tension between Washington and Tehran, at odds over a range of issues from Iran’s nuclear programme to US allegations of Iranian support for terrorism.

Oil prices briefly rose on the news about the confrontation as dealers weighed the threat to oil shipments along the key shipping route. Crude futures jumped 49 cents to $98.40 a barrel before slipping back.

Pentagon spokesman Bryan Whitman said the three US ships had been in international waters passing through the Strait of Hormuz on Sunday when they were approached by five fast boats, some of which were visibly armed.

The boats were identified as Iranian and “made some aggressive maneuvers against our vessels and indicated some hostile intent”, Whitman said.

“This required our vessels to issue warnings and conduct evasive maneuvering,” Whitman told reporters. “The US Navy vessels were prepared to take appropriate actions... but there was no engagement of the vessels.”

Other Pentagon officials said the Iranians made threats by radio and a US captain was in the process of ordering sailors to open fire when the Iranian boats moved away.