US officials have confirmed that the unmanned surveillance plane lost in Iran, is a stealth aircraft used for secret missions by the CIA.

Officials said Iran's military appears to be in possession of the aircraft, which was shaped and designed to evade enemy defences. The mission of the downed drone remains unclear.

The RQ-170 has been used by the CIA for highly sensitive missions in surveillance operations against other countries. US officials have acknowledged that the military lost control of one of its stealth drones while it was flying a mission over western Afghanistan.

Iran's official I-R-N-A news agency said the country's armed forces shot it down. But the US rejected the claim, saying there are no indications the plane was shot down.