Senior Defense Department officials said Monday they have no knowledge of any U.S. drone flights over Iran, and U.S. intelligence officials would not comment on any such flights.
The responses came one day after the Washington Post ran a story saying that the United States has been running unmanned spy flights over Iran for the past year for evidence of nuclear weapons programs and to probe air defenses.
The Iranian government has lodged a protest with Washington over the matter through Swiss channels since the two nations have no formal diplomatic relations, the Post said.
But a defense official at the Pentagon (search) told FOX News that "the story has a lot of people scratching their heads in this building.
"We're not the only ones who fly those things," the official said.
The U.S. intelligence community has its own fleet of unmanned drones. The U.S military did confirm that it has been operating unmanned and manned flights along the Iraq-Iran border to assist local border patrol in Iraq.
In the Post story, three sources identified as U.S. officials with knowledge of the effort said the small, pilotless planes use radar, video, still photography and air filters designed to pick up traces of nuclear activity to gather details not accessible by satellites.
It reported that one U.S. official acknowledged that drones (search) were being used, but that the Iranian complaint focused on manned military aircraft overflights, which the United States denied.
Iranians living along the Caspian Sea and on the Iraq border first started reporting sightings of UFOs in late December, according to Iranian newspaper reports. Eyewitnesses commonly reported red flashes, streaks of green and blue and low lights that quickly disappeared. The Iranian air force determined from the reports that the lights were spy drones, the Post reported, adding that Iranian officers are familiar with U.S. tactics since being trained in the United States more than 25 years ago.
The Post quoted an unidentified senior Iranian official as saying Iran's National Security Council decided not to engage the pilotless aircraft because it did not want to reveal the country's air defense capabilities. The decision is considered a major policy move to demonstrate the council's belief that an attack is unlikely anytime soon, the newspaper said.
Asked about the Iranians' restraint, one senior defense official said: "If you think the Iranians would not shoot the drones down, you're smoking something."
U.S. military commanders point out that the flights would be very risky since Predator (search) and other drones are very slow and could easily be shot down. A crash, which is not uncommon for drones, could also present a host of problems.
Word of the drones comes on the heels of stepped-up calls by the Bush administration for Iran to submit to international observation of its nuclear activity to ensure that it is not developing nuclear weapons.
The U.S. government believes Iran is using its nuclear energy program to conceal an effort to manufacture nuclear weapons and is relying, for the time being, on France, Britain and Germany to negotiate curbs on any such efforts.
The Post said U.S. officials confirmed that the drones were deployed along Iran's northern and western borders, first in April 2004 and again in December and January.
FOX News' Bret Baier and Nick Simeone and The Associated Press contributed to this report.