Iran's Revolutionary Guards said on Saturday that the US Navy had approached their patrol vessels in the Arabian Gulf and fired flares in what it called a provocative move.
"At 4 pm (1130 GMT) on Friday, the supercarrier USS Nimitz and its accompanying warship, while being monitored by the Guards' frigates, flew a helicopter near the Resalat oil and gas platform and approached the force's ships," the Guards said.
"The Americans in a provocative and unprofessional move, sent a warning message to the frigates and fired flares."
The Guards "ignored the unconventional move by the US ships and continued their mission, after which the supercarrier and its warship left the area," the statement added.
On Tuesday, a US Navy patrol ship fired warning shots at a Guards boat in the Gulf as it closed in on the American vessel, US officials said.
According to a press release from a US Navy spokesperson on the incident on Friday, “While conducting a routine patrol in the international airspace of the Arabian Gulf on July 28, a US Navy helicopter observed several Islamic Revolutionary Guard Corps naval vessels approaching US naval forces at a high rate of speed. US naval forces attempted to establish communications, with no response from the Iranian vessels. Shortly thereafter, at a safe distance, the US helicopter deployed flares, after which the Iranian vessels halted their approach.”
“Following communications, the Iranian vessels were observed conducting a gun exercise,” the release said.
US Naval Forces Central Command “assesses the interaction as safe and professional,” it concluded.
The Guards denied approaching the US ship on that occasion and said it was the American vessel that had been at fault.
There have been a string of close encounters between US ships and Iranian vessels in the Gulf in recent months.
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, which connects it to the Indian Ocean.
The Revolutionary Guards are a paramilitary force that answers directly to Iran's supreme leader Ayatollah Ali Khamenei.
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.
The latest incident comes after the US Congress approved new sanctions against Iran.