Three Royal Navy ships were forced to change their course after they were "unsafely" approached by Iranian vessels, officials say.
The ships were accompanying US Navy tracking ship USNS Invincible in the Strait of Hormuz on Saturday when they were approached by a number of fast-attack vessels from the Iranian Revolutionary Guard Corps, a US official told Reuters.
The official said the boats attempted to get between the Royal Navy ships and USNS Invincible, before stopping within 600 yards of the US ship.
He added that attempts were made to communicate over radio, but there was no response and the interaction was "unsafe and unprofessional".
A Royal Navy spokesperson told Sky News the British ships were in the strait "as part of our commitment to maintain security and stability in the region", adding that crews "are well trained to deal with a variety of scenarios".
Stand-offs between US ships and Iranian vessels have become a regular occurrence on the Strait of Hormuz, which is a narrow passage that leads from the Persian Gulf to the Arabian Sea.
A large portion of the world's oil passes through the strait on tankers, making it a strategically important route.
In January, a United States Navy destroyer fired warning shots at four fast-attack Iranian patrol boats which came within 800m of the ship.
During his presidential campaign, Donald Trump vowed that Iranian ships which intimidate the US Navy would be "shot out the water" under his rule.
And, responding to the Iranian test of a new ballistic missile last month, he warned Tehran it was "playing with fire".