This video grab image ? obtained July 25, 2017, courtesy of the US Navy ? shows an IRGCN boat heading towards the USS Thunderbolt in the Gulf. AFP/US Navy/Handout

WASHINGTON: A US Navy patrol ship fired warning shots Tuesday at an Iranian Revolutionary Guard Corps boat in the Persian Gulf as it closed in on the American vessel, officials said.

The shots were fired after the Iranian vessel came to within 150 yards of the USS Thunderbolt and failed to respond to repeated attempts to reach it via radio, then ignored warning flares and a series of blasts on the US ship's whistle, the Navy said in a statement.

"The Iranian vessel's actions were not in accordance with the internationally recognised? 'rules of the road' nor internationally recognised maritime customs, creating a risk for collision," the statement read, noting that the Iranians had conducted an "unsafe and unprofessional" interaction.

The incident occurred at about 3:00 AM local time (0500 PST) in the northern Persian Gulf. After the US ship fired the warning shots, the Iranian vessel stopped, officials 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 Corps is a paramilitary force that answers directly to the Islamic republic's supreme leader.

The force's boats periodically approach US warships in international waters and the Strait of Hormuz, ignoring US radio messages and giving little indication of their intentions.

In January 2016, the Iranians briefly captured the crew of two small US patrol boats that strayed into Iranian waters.

The 10 US sailors were released 24 hours later.

Tuesday's incident comes as the US Congress votes on a new sanctions bill against Russia.

The measure also includes sanctions against Iran and the IRGC navy ? which stands accused of supporting terrorism ? and North Korea, for its missile tests.