The unmanned surveillance plane lost by the United States in Iran was a stealth aircraft being used for secret missions by the CIA, U.S. officials said Monday, December 5.

The officials said Iran’s military appears to be in possession of one of the more sensitive surveillance platforms in the CIA’s fleet, an aircraft that was shaped and designed to evade enemy defenses.

The mission of the downed drone remains unclear. Iran, a longtime adversary of the United States, is believed by U.S. intelligence agencies to be pursuing the development of a nuclear weapon and is also accused of providing support to anti-coalition elements in both Iraq and Afghanistan.

The RQ-170 has been used by the CIA for highly sensitive missions into other nations’ airspace, including months of surveillance of the compound in Pakistan in which Osama bin Laden was hiding before he was killed in a May raid by Special Operations forces.

The disclosure that the drone apparently recovered by Iran was being flown by the CIA comes after previous signals from U.S. officials that had created the impression that the plane was being flown by the U.S. military on a more mundane mission over Afghanistan and had simply strayed into Iranian territory, Washingtonpost reported.