Iran's Islamic Revolution Guards Corps (IRGC) said the aircraft had violated Iranian airspace, and that the incident sent a "clear message to America".
But the US military insisted the drone had been over international waters at the time, and condemned what it called an "unprovoked attack" by the IRGC.
President Donald Trump tweeted: "Iran made a very big mistake!"
President Donald Trump has played down the significance of Iran shooting down a US drone over the Gulf, saying he found it “hard to believe” the move was intentional, only hours after he had warned that Tehran had made a “very big mistake”.
“I find it hard to believe it was intentional,” Mr Trump said on Thursday while receiving Justin Trudeau, Canadian prime minister, at the White House. “It could have been somebody who was loose and stupid that did it . . . But it was a very foolish move.”
ABout-face: President Donald J. Trump made a last-minute decision to call off strikes against Iran in response to the downing of a drone.
President Donald Trump approved a plan to use military force against Iran but canceled it after it was underway, according to news outlets.