US ship fires warning shots at Iran vessel in Gulf standoff

A US navy patrol ship fired warning shots at an Iranian Revolutionary Guard naval vessel in the Gulf on Tuesday after it came within 100 metres, a US defence official said. 

"The IRGCN boat was coming in at a high rate of speed," the US defence official told AFP on the condition of anonymity.

"It did not respond to any signals, they did not respond to any bridge-to-bridge calls, they felt there was no choice except to fire the warning shots."

The incident occurred at about 3am local time in the northern Gulf when the Iranian vessel began to approach the USS Thunderbolt.

Prior to firing warning shots, the American navy ship had also fired flares to warn the Iranian vessel, according to the AP news agency. 

After the US ship fired the warning shots, the Iranian vessel stopped, the official said, at which point the Thunderbolt continued on her way.

The episode marks the latest in a series of close encounters between US ships and Iranian naval vessels.

In January, the USS Mahan destroyer fired warning shots at four Iranian Revolutionary Guard vessels that approached at high speed in the Strait of Hormuz.

The Iranian Revolutionary Guards are a paramilitary force that answers directly to the Islamic republic's supreme leader.