NATO has implicitly denied that the Iranians shot down their spyplane. It claims, however, that the pilots "lost control" of the plane late last week and it's missing.
It hasn't confirmed the model but it says this is the lost plane the Iranians are referring to.
NATO published the information in a very brief official statement released by the International Security Assistance Force in Afghanistan:
The UAV to which the Iranians are referring may be a US unarmed reconnaissance aircraft that had been flying a mission over western Afghanistan late last week. The operators of the UAV lost control of the aircraft and had been working to determine its status.
There are no more details at this time. [ISAF]