President Barack Obama acknowledged for the first time Monday that a US drone was in Iranian hands and said the United States has asked Tehran to return the sophisticated spycraft.

"We've asked for it back. We'll see how the Iranians respond," Obama said at a news conference with Iraqi Prime Minister Nuri al-Maliki.

It was the first open confirmation by the Obama administration that Iran was in possession of the drone, which Tehran says it brought down as the plane was flying over its territory.

Obama, however, shed no further light on the plane's mission or why it failed to return to a base in Afghanistan.

"With respect to the drone inside of Iran, I'm not going to comment on intelligence matters that are classified," he said.

US Secretary of State Hillary Clinton said the United States had made a "formal request" to Tehran to return the drone but expressed doubt the arch-US foe would do so.

"Given Iran's behavior to date, we do not expect them to comply," Clinton told reporters at a press conference with British Foreign Secretary William Hague, with whom she discussed Iran.

The bat-winged RQ-170 Sentinel, a stealth drone designed to evade radar for surveillance flights, was on a CIA mission when it went missing, US officials, speaking anonymously, had said previously.

The episode has handed Iran a propaganda coup and Iranian state television has shown images of a robotic aircraft that experts say resembles the Sentinel.

Iran has vowed to reverse engineer the drone but has given contradictory accounts of how the aircraft went down on December 4. Tehran initially said it shot down the drone but later claimed the Iranian military managed to hack into the plane's flight controls.

Defense Secretary Leon Panetta voiced skepticism that Iran would manage to gain much of a technological advantage from the aircraft.

"It's a little difficult to know just frankly how much they're going to be able to get from having obtained those parts," Panetta told reporters aboard a US military aircraft.

"I don't know the conditions of those parts. I don't know what state they're in."

Asked if Iran may have forced the plane down in a cyber-attack, Panetta said: "I don't know."

US officials previously indicated it was more likely the drone suffered a malfunction.

Other American drones have flown off-course in the past, including the Fire Scout robotic helicopter, with which engineers lost contact during a 2010 flight in Maryland.

Military commanders at one point considered shooting the helicopter down as it was heading toward the US capital but technicians managed to regain control of the aircraft.

US officials and analysts also have cast doubt over Iran's ability to replicate the drone -- at least without the help of Russia or China.

"US capabilities are remarkably advanced, and it's unclear that the Iranians have the expertise" to exploit the advanced technology -- including sensors -- in the aircraft, a US official told AFP on condition of anonymity.

Former vice president Dick Cheney meanwhile criticized Obama, saying the president should have ordered an air strike to quickly destroy the drone to prevent Iran from examining the high-tech aircraft.

"The right response to that would have been to go in immediately after it had gone down and destroy it," Cheney said an interview with CNN.

"You can do that from the air. You can do that with a quick air strike. And, in effect, make it impossible for them to benefit from having captured that drone," Cheney told CNN's "Erin Burnett OutFront" program.