Iran says the US has been flying unmanned surveillance drones over the country's nuclear sites.
Iran denies claims that it wants to build nuclear weapons
Such spying activities have been going on for a "long time", said Intelligence Minister Ali Yunesi.
He said the air force had been ordered to shoot down any unknown or suspicious aircraft in Iranian airspace.
"Most of the shining objects that our people see over Iran's airspace are American spying equipment used to spy on Iran's nuclear facilities," he said.
His comments follow a recent Washington Post report quoting an anonymous American official as saying that US drones had been flying across Iran, seeking evidence of nuclear weapons development.
The US accuses Iran of seeking nuclear weapons but Iran denies this, saying that its nuclear development programme is purely for peaceful, energy-generating purposes.
The country's state-run media has been reporting numerous sightings of unidentified flying objects near nuclear facilities.