An Iranian military commander said today that the Islamic republic is building a copy of a US spy drone captured in December 2011 and revealed what he said were "codes" gleaned from the unmanned aircraft.

"I am giving you four codes so the Americans understand just how far we have gone in penetrating the drone's secrets," General Amir Ali Hajizadeh, the head of the Revolutionary Guards' aerospatial division, told state television.

"In October 2010, the aircraft was sent to California for some technical issues, where it was repaired and after flight tests, it was taken to Kandahar (in Afghanistan) in November 2010, when a series of technical problems still prevailed," he said.

"In December 2010, it was sent to an airport near Los Angeles for repair of its equipment and sensors, and flight tests. The drone was then sent back to Kandahar," he said.

Hajizadeh did not give further details, saying: "This aircraft is a national treasure for us, and I cannot divulge information about it."

But he added Iran has "started producing a copy of the RQ-170 drone," stressing it used the same US technology in stealth fighters and bombers.

The unmanned, bat-winged RQ-170 went down in Iran four months ago, and Iran's gleeful military proudly displayed it on state television apparently intact, though with what appeared to be damage to one of its wings.

Iran claimed one of its cyberwarfare team hacked its controls by confusing its GPS guidance system, and said it would reverse-engineer the drone to make its own.

US officials admitted they lost the drone on a CIA mission over Iran, but asserted the stealth aircraft came down because of a technical problem, not Iranian intervention.

While US President Barack Obama made a vain request for Iran to return the drone, his defence secretary, Leon Panetta, voiced scepticism over how much technological knowledge Tehran could gain from the aircraft.