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.