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

"As always it was a complex tactical picture, we believe two drones. We believe two drones were successfully - there may have been more that we are not aware of - those are the two that we engaged successfully," McKenzie said.

CBS said the drones were reportedly brought down by an electronic signal or pulse that disabled their flight controls. One drone disappeared from US military radars while the second was seen hitting the water.

Iran, which last month shot down a US Predator 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 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 strategically vital waterway, 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 Gulf into a powder keg.