Iran's elite Revolutionary Guard said a US navy aircraft carrier fired a warning shot in an "unprofessional" confrontation with Iranian vessels, the official IRNA news agency has reported.

IRNA quoted a statement as saying that the USS Nimitz and an accompanying ship came near an Iranian oil offshore platform in the Persian Gulf and a helicopter from the ship hovered near vessels manned by Iran's elite Revolutionary Guard.

The report said the confrontation took place on Friday afternoon and the US navy ships left the area following the encounter.

The incident comes after a US navy patrol boat fired warning shots on Tuesday near an Iranian vessel that American sailors said came dangerously close to them during a tense encounter.

Iran and the US frequently have run-ins in the Persian Gulf, nearly all involving the Revolutionary Guard, a separate force from Iran's military which answers only to the country's supreme leader.

In January, near the end of then-president Barack Obama's term, the USS Mahan fired shots toward Iranian fast-attack boats as they neared the destroyer in the Strait of Hormuz.

Iranian forces view the American presence in the Gulf as a provocation. They have accused the US navy of unprofessional behaviour, especially in the Strait of Hormuz, the mouth of the Persian Gulf through which a third of all oil trade passes by sea.