"We are confident we brought down one drone, we may have brought down a second," US Central Command chief General Kenneth McKenzie told CBS news in an interview aboard the USS Boxer, the vessel at the center of the incident.

A spokesman for CENTCOM, Lieutenant Colonel Earl Brown, later said that the ship had carried out a "defensive action" after "aggressive interactions by two Iranian (drones) in international waters."

"We observed one (drone) crash into the water but did not observe a 'splash' for the other," he said.

"The United States reserves the right to defend our personnel, facilities, and interests and calls upon all nations to condemn any attempts to disrupt freedom of navigation and global commerce," Brown added.

CBS said the drones were reportedly brought down by an electronic signal or pulse that disabled their flight controls.

Iran, which last month shot down a US Global Hawk drone that it said had ventured into its airspace, has denied that it lost any of its own unmanned aerial vehicles, after President Donald Trump announced that the USS Boxer had downed one.

Amid soaring tensions in the region, Trump said in late June that he had called off strikes against Iran at the last minute in response to the destruction of the US drone.

A series of attacks on oil tankers in the Gulf region, as well as Iran's seizure of a British-flagged tanker in retaliation for Britain impounding one of its own vessels in Gibraltar, have turned the area into a powder keg.