A US Navy destroyer fired three warning shots at four of Iran's Islamic Revolutionary Guard Corps vessels after they closed in at a high rate of speed in the Strait of Hormuz, two U.S. defence officials told Reuters today.

The officials, speaking on the condition of anonymity, said the USS Mahan established radio communication with the boats but they did not respond to requests to slow down and instead continued asking the Mahan questions. The Navy destroyer fired warning flares and a US Navy helicopter also dropped a smoke float before the warning shots were fired.

The Iranian vessels came within 800 meters of the Mahan, which was escorting two other US military ships, they said.

The IRGC was not immediately available for comment.

The incident comes as President-elect Donald Trump is about to take office on January 20. In September, Trump vowed that any Iranian vessels that harass the US Navy in the Gulf would be "shot out of the water."

One official said similar incidents occur occasionally. Most recently in August, another US Navy ship fired warning shots towards an Iranian fast-attack craft that approached two US ships.

The official added that the warning shots were just one of seven interactions the Mahan had with Iranian vessels over the weekend, but the others were judged to be safe.