"What I don't like about that is they [Iranian boats] were in the middle of international transit waters"
US Navy commanders accused Iran of jeopardising international navigation by "harassing" warships passing through the Strait of Hormuz and said future incidents could result in miscalculation and lead to an armed clash.
They spoke after the US aircraft carrier George H W Bush confronted what one of the commanding officers described as two sets of Iranian Navy fast-attack boats that had approached a US-led, five-vessel flotilla as it entered the Strait on Tuesday on a journey from the Indian Ocean into the Gulf.
It was the first time a US carrier entered the narrow waterway, where up to 30 percent of global oil exports pass annually, since President Donald Trump took office in January pledging a tougher US stance towards Iran.
US commanders said Tuesday's incident, in which the George H W Bush sent helicopter gunships to hover over the Iranian speedboats as some came as close as 950 yards (870 metres) away from the aircraft carrier, ended without a shot being fired.
But it underscored growing tension between the United States and Iran since the election of Trump, who has condemned the 2015 nuclear deal that his predecessor Barack Obama and leaders of five other world powers struck with Tehran and labelled the Islamic Republic "the number one terrorist state."
The encounter with Iranian Navy boats occurred as the USS George H W Bush was en route to the northern part of the Gulf to participate in U.S.-led air strikes against Islamic State militants in Iraq and Syria.
"What I don't like about that is they [Iranian boats] were in the middle of international transit waters [while] we had a right to be there as we were exercising freedom of navigation on our way into the Arabian Gulf," Rear Admiral Kenneth Whitesell, commander of the Carrier Strike Group 2, told journalists aboard the aircraft carrier.
"They also had weapons uncovered as some of the cameras were able to tell. They had some of the weapons manned. We also have aerial data that they were arming all of these weapons."
Whitesell said Iran's position was that the US-led flotilla, which included a Danish frigate and a French destroyer, had breached its territorial waters, which he denied.
There was no immediate comment from Tehran.
In another incident, Iran's Revolutionary Guards said a US Navy ship changed course towards Iranian vessels in the Strait of Hormuz on March 4 and accused Washington of "unprofessional actions ... [that] can have irreversible consequences".
A US official told Reuters on March 6 that multiple fast-attack vessels from the Revolutionary Guards had come within 600 yards (550 meters) of the USNS Invincible, a tracking ship, forcing it to change direction.
Years of mutual animosity eased when Washington lifted sanctions on Tehran last year after the deal to curb Iran's nuclear ambitions. But strong differences remain over Iran's ballistic missile programme and conflicts in Syria and Iraq.
Captain Will Pennington, commanding officer of the George H W Bush, told Reuters that the behaviour of the Iranian navy had become "more aggressive and less predictable".