"The planes that were shot down are among the most modern US navy drones and have a long-range capability," Ali Fadavi, commander of Guards' naval forces, was quoted as saying by Fars news agency.
On 2 January, the head of Guards air force said the elite unit had downed two "Western spy" drones. He had not said when the two drones were actually shot down.
"These aircraft are in our possession and at an appropriate time they will be displayed" to the public, Fadavi said, rejecting Western media reports that quoted Washington officials denying the drones were shot down by Iranian forces.
"It is natural that they don't accept or reject such matters. What is certain is that the Revolutionary Guards did this," Fadavi added.
The US navy's Fifth Fleet is based in Bahrain, just across the Arabian Gulf from Iran.
Iranian commanders have repeatedly threatened to block navigation through the strategic Strait of Hormuz, which links the Gulf to the Indian Ocean, if the Islamic republic comes under attack.
Forty per cent of the world's oil supplies pass through the strait.
The US military and Central Intelligence Agency regularly use drones to launch missile strikes in Afghanistan and in Pakistan's tribal belt, but do not generally confirm attacks.
Iran's Revolutionary Guard Corps, target of a series of US sanctions, was set up as a force to defend the 1979 Islamic revolution from internal and external threats.
Washington imposed fresh sanctions against the Guards last month in a bid to ramp up pressure on Tehran over a controversial nuclear programme that Iran says is entirely peaceful, but which world powers suspect is aimed at building an atomic bomb.