The Lockheed Martin RQ-170 Sentinel is one of the most advanced stealth aeroplanes in the United States Air Force. It was secret drone until the end of 2009. The iranians just claimed today they have killed one.
The Iran military claim that the downed plane has little damage. They say it was not shot down by jet fighters or ground defences, but using some kind of electronic interference:
The informed source said on Sunday that Iran Army's electronic warfare unit successfully targeted the American-built RQ-170 Sentinel stealth aircraft after it crossed into Iranian airspace over the border with neighbouring Afghanistan.
The Iranians have claimed US drone kills many times, although they have never produced much proof of their claims. They haven't shown any picture of the downed RQ-170 Sentinel. If they really killed it, I would imagine that they would like to brag about it with videos and pictures. On the other hand, if their "mostly intact" claims are true and they show it, then the US could demand that they return their highly-valued property. [IRNA (Translated) via Flight Global]