Iran denied on Saturday U.S. accusations that its fast-attack boats were “harassing” warships at the mouth of the Gulf, and said Washington would be responsible for any clashes in the key oil shipping route.

U.S. Navy commanders earlier accused Iran of jeopardizing 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 U.S. 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 U.S.-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 U.S. carrier entered the narrow waterway, where up to 30 percent of global oil exports pass, since President Donald Trump took office in January pledging a tougher U.S. stance towards Iran.

In Tehran, Brigadier General Masoud Jazayeri, deputy chief of staff of Iran’s armed forces, said the U.S. claims of the confrontation in the Gulf were based on “false reports or ulterior motives”, the state news agency IRNA reported.

“We emphasize that the Americans would be responsible for any unrest in the Persian Gulf, and again warn that the U.S. military must change its behavior,” Jazayeri said, without elaborating.

U.S. commanders earlier 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 meters) 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 labeled 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.

Earlier in March, Iran disputed the U.S. account of another confrontation in the Strait of Hormuz between its speedboats and a U.S. Navy vessel. {nL5N1GL1SL]

(Reporting by Dubai newsroom; Editing by Helen Popper)