A US Navy ship fired warning shots at Iranian boats ' title=' at Iranian boats '>at Iranian boats near the Strait of Hormuz, a US official said on Monday.

Iranian vessels on Sunday approached a US Navy ship at high speed near the strait in five separate instances, CNN quoted the official as saying.

The USS Mahan tried to tell the Iranian Islamic Revolutionary Guard boats to stop via radio communication, but the vessels didn't respond to the request, prompting the destroyer to fire three warning flares, said the official.

In addition, a Navy helicopter dropped a smoke float.

The Iranian boats approached to within 900 yards of the Mahan, which had been escorting two US ships, according to reports.
 

In recent days, Iran's Revolutionary Guard Corps has conducted an annual exercise in the strait simulating manoeuvres necessary to shut down the entrance to the Persian Gulf.

The incident is the latest tense encounter between the two countries in and over waters near Iran over the past few months.

These brushes have included Iranian rocket launches, drones flying over US vessels and the capture of US sailors.