WATCH: The US Navy released footage of the alleged incident.
The US Navy has accused Iran of carrying out "dangerous and harassing" approaches to several American ships operating in international waters in the Persian Gulf.
It says 11 Iranian vessels repeatedly provoked six US ships involved in military operations near Kuwait, passing close to them at high speed.
USS Lewis B. Puller, USS Paul Hamilton, USS Firebolt, USS Sirocco, USCGC Wrangell and USCGC Maui were said to have been conducting joint-service operations with US Army attack helicopters, when they repeatedly crossed paths with Iranian Islamic Revolutionary Guard Corps Navy (IRGCN) vessels.
The United States says the boats "crossed the bows and sterns" of the American ships in the international waters, coming within 10 yards of USCGC Maui and 50 yards of USS Lewis B. Puller.
The incident was said to have lasted one hour, after several warning sounds from the American ships.
The US has accused the Iranians of violating the international "rules of the road" and said they retained the right to act in self-defence.
"The IRGCN's dangerous and provocative actions increased the risk of miscalculation and collision," they added.
There was no immediate comment from Iranian officials.
Tense incidents remain common between Tehran and Washington’s forces in the Persian Gulf and its narrow mouth called the Strait of Hormuz, through which a fifth of the world’s oil passes.
British shipping has been targeted by Iran since tensions peaked last summer, which saw the Islamic Revolutionary Guard seize a British-flagged tanker.
Cover image: A US Navy photograph appearing to show Iranian vessels sailing close to US forces (Picture: US Department of Defense).