Early reports by NATO said that they were missing a drone. At the same time officials claimed that there was no evidence that Iran shot the drone down as they had claimed. ISAF(International Security Assistance Force) officials joined in the game of misleading the public.
The drone ISAF said was a U.S. unarmed reconnaisance aircraft on a mission over Afghanistan. So the mystery is explained. The U.S. launches many drone missions over Afghanistan and this drone just wandered off course.
Not mentioned is that this was a special drone. Not mentioned is that this was operated by the CIA. Not mentioned is that there has been secret spying missions over Iran for some time now. See this article.
The drone is not a garden variety reconassaince drone but a special secret stealth drone the RQ-170. The same drone was used to spy on bin Laden's compound in Pakistan before it was raided by U.S. special forces.
Apparently the U.S. has an air base at Shindad in Afghanistan from which it can launch surveillance missions and even special operations into Iran should the U.S. decide to do so. Sources say that they have contingency plans to mount secret operations into Iran should the need arise.
According to the Belfast Telegraph the U.S. is running covert operations in Iran already. Republican presidential candidate has called not only for covert operations but also attacks on Iranian oil refinieries. With talk like that surely Iran has good grounds for attacking the U.S in self defense. Of course it will not. Only the stronger party can actually engage in that sort of action and then claim self defense. For more see this article