President Donald Trump has said the US Navy destroyed an Iranian drone in the Strait of Hormuz.
He said the USS Boxer amphibious assault ship “took defensive action” on Thursday after the drone came within about 1,000 yards (914m) of the vessel.
Iran said it had no information about losing a drone. In June, Iran downed a US military drone in the area.
Earlier, Tehran said it had seized a “foreign tanker” and its 12 crew on Sunday for smuggling fuel in the Gulf.
Iran has been blamed by the US for attacks on tankers since May in the world’s key shipping area. Tehran denies all the accusations.
The recent incidents have triggered fears of a military conflict in the region.
Washington earlier said Iran must immediately release the tanker it said it had seized.
Iran’s state media quoted Iran’s Revolutionary Guards as saying the vessel had been smuggling one million litres (220,000 gallons) of fuel.
The state media later published footage of Iranian speedboats circling around the Panamanian-flagged Riah tanker.
The tanker was seized south of Iran’s Larak Island, Iran said.