Intelligence Minister Ali Yunesi comments backed a report in The Washington Post on Sunday that quoted unnamed U.S. officials as saying the drones have been flying over Iran for nearly a year to seek evidence of nuclear weapons programs.
"U.S. spying activities over Iranian airspace have been going since a long time ago," Yunesi told reporters.
"Most of the shining objects that our people see in Iran's airspace are American spying equipment used to spy on Iran's nuclear and military facilities," the minister told reporters.
Iranian media has been gripped by a kind of "flying object" fever with dozens of reported sightings in recent weeks. State-run media has reported numerous sightings of unknown objects flying over parts of Iran where nuclear facilities are located.
In an incident on Wednesday, there were reports of anti-aircraft fire and an explosion near the town of Deilam, about 60 miles from a nuclear facility. Iranian state television later said that the explosion may have been caused by a fuel tank dropping from an Iranian plane.
In speaking to reporters, the Iranian minister said U.S. surveillance flights would not reveal anything the United States doesn't already know.
"Our nuclear activities are open and very transparent. Our military activities are all legal," Yunesi said. He spoke while visiting a prison for dissidents under the Shah that has been turned into a museum.
The Washington Post reported the drones had been flying over Iran from U.S. military bases in Iraq and were equipped with air filters to pick up traces of nuclear activity.
In December, the Iranian air force was ordered to shoot down any unknown flying objects. At the time, there were reports in Iranian newspapers that Iran had discovered spying devices in pilotless planes its air defense force had shot down.
"If any of the bright objects come close, they will definitely meet our fire and will be shot down. We possess the necessary equipment to confront them," Yunesi said.
Last month, Yunesi said the United States had been conducting aerial surveillance, but he neither mentioned drones nor nuclear and military sites. Yunesi said U.S. commandoes had not entered Iran, adding the security forces would catch any American who did.
The unidentified objects described by Iranian media were spotted near Natanz — which has a uranium enrichment plant — and Isfahan, which has a facility for producing uranium hexaflouride gas, the feedstock for enriching uranium.
Uranium enriched to low grades is used for fuel in nuclear reactors. Further enrichment makes it suitable for atomic bombs.
The United States accuses Iran of having a secret program to manufacture nuclear weapons. Iran denies this, saying its nuclear program is entirely for the generation of electricity.
Middle East expert and Brooking Instituion Senior Fellow Shibley Telhami says a nuclear Iran poses new questions for the United States and Israel.
"Military option remain very very limited for the U.S. and Israel," Telhami said. "It is clear that Iran is not Iraq, Iran has far more potential militarily. It is clear they have learned the lesson of the 1980 Israeli attack on the Iraqi nuclear reactor and most likely have dispersed their assets. I think in the short term, the reality remains military option is very limited, very dangerous and has got a lot of consequences."