"There is absolutely no precedence for this. This is the first time that a [drone] has been fired upon to our knowledge by Iranian aircraft," said Mr. Little.
When he was asked if the Iranians might have fired only warning shots, Little replied: "Our working assumption is that they fired to take it down. You'll have to ask Iranians why they engaged in this action."
While both sides have engaged in heated rhetoric over Iran's controversial nuclear program, neither announced the drone incident last week until CNN broke the news on Thursday.
CNN reported a senior US official saying: "At least two bursts of gunfire came from the Su-25s' cannons. The drone started to move away but the Iranian aircraft chased it, doing aerial loops around it before breaking away and returning to Iran."
At a press briefing Thursday, Little said the Pentagon considered media reports "an unauthorized disclosure of classified information," and that the US military did not announce the Nov. 1 incident because "we routinely do not advertise our classified surveillance missions."
There was no way to independently confirm the Pentagon's account, and correct facts have not always been initially forthcoming in past US-Iran incidents in the Persian Gulf.
The Pentagon announced in January 2008, for example, that several of its warships had been harassed by five armed Iranian speed boats. It released a video of the incident, in which a voice was heard to say: "I am coming at you. You will explode...."
The Pentagon first announced that US officers – after seeing suspicious packages dropped into the water – were on the verge of opening fire; one ship commander later denied that.