Iran says its armed forces have shot down an unmanned American spy plane over eastern Iran and it will retaliate if there are any further violations of their air space.
Media reports said the drone - identified as a type RQ170 - had minor damage and was in Iran's possession.
NAT0 says it could be one that was lost over western Afghanistan last week.
Iran said in July it had shot down a drone over the holy city of Qom, near a nuclear site.
Last January, it said it downed two "Western spy drones" in the Gulf, but produced no evidence to support the report.