Iranian state television on Thursday broadcast footage of Revolutionary Guard boats appearing to chase off what it said were US naval vessels.
"These images show force and total control in the face of American and foreign forces in the Persian Gulf," it said, without giving a date or exact location.
The US Fifth Fleet, which is based in Bahrain, said it had no information of any such recent incident.
"There was no unsafe or unprofessional interaction involving the US Navy in the past 48 hours," said spokesman Lieutenant Commander Tim Hawkins.
Iranian television did not specify when the footage was filmed.
In the video, a Guard is heard calling out "Follow them", "Take photos" and "Call our boat to come back".
The footage, filmed from a speedboat, appears to show it pursuing naval vessels, one of them flying the US flag.
The broadcast came on the day the Guards, an elite unit of Iran's military, mark their navy day.
US and Iranian naval vessels have been involved in several tense incidents in the past.
In April 2020, the US navy protested over "dangerous" manoeuvres by the Revolutionary Guards which had steered too close to one of its ships.