The Pentagon has accused the Iranian navy of "unsafe and unprofessional" conduct after allegedly flying a helicopter within about 25 yards of a US warship.
Pentagon Press Secretary John Kirby said the incident, which happened in the Gulf of Oman last week, risked escalation and that the helicopter circled the American vessel three times.
Video shared on social media appears to show a helicopter flying close to a US Navy warship.
Mr Kirby confirmed to reporters that an Iranian navy helicopter had flown close to amphibious assault vessel USS Essex, at one point flying "about 10 feet off the surface of the ocean".
"Without getting into specifics, the crew of the Essex took the appropriate force protection measures that they felt they needed to, and they acted, of course, in accordance with international law.
"There was no impact ultimately to the Essex transit or their operations. But that doesn't mean that this wasn't an unsafe and unprofessional act.
"Again, I'll say it again, we're going to act in accordance with international law, we're going to fly, sail, and operate where international law permits. And we're going to continue to look after our national security interests in the region."
Mr Kirby said the incident was "dangerous" because it could have led to "miscalculation".
"When you have another armed force, in this case, the Iranian navy that flies like this, you definitely run the risk of some sort of escalation and a miscalculation, or on either side here, and that's not helpful.
Watch: An "unsafe" incident involving US and Iranian ships in the Persian Gulf in April.
"This one ended peacefully, but it doesn't mean it was safe and professional. It absolutely wasn't."
Mr Kirby refused to go into more detail about what "force protection measures" the commanding officer of the USS Essex took but said "he did what he believed was in the best interest of his ship and his crew".
He also said "questions really should be asked of Tehran and the Iranian navy" over "why they felt this was a prudent use of their pilots in their aircraft".
Last week, Royal Navy aircraft carrier HMS Queen Elizabeth - which is leading the UK's Carrier Strike Group deployment - worked alongside the USS Essex, cross-decking aircraft.
The incident follows reports earlier this month that drones, believed to be Iranian, had come close to the Essex in the Strait of Hormuz.
Tensions between Iran and the US have been heightened following former president Donald Trump's unilateral withdrawal of America from Iran's 2015 nuclear deal with world powers.
There have also been flashpoints of tension between the UK and Iran, notably the seizing of the British-flagged tanker Stena Impero by Iran's Revolutionary Guards Corps in 2019.