|Iran's Fars news agency said the drone had been brought down after it violated the country's airspace [Fars website]
A surveillance drone flying over western Afghanistan had gone out of control late last week and may be the one Iran said it had shot down over its own airspace, the International Security Assistance Force (ISAF) has said.
"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," an ISAF statement said on Sunday.
The statement was issued in Kabul and released to reporters covering an international conference on Afghanistan in the German city Bonn.
A US official told the Reuters news agency that there is "absolutely no indication" up to this point that the drone that crashed in Iran was shot down.
Iranian media reported on Sunday that its forces had brought down an unmanned US spy plane.
"Iran's military has downed an intruding RQ-170 American drone in eastern Iran," Iran's Arabic-language Al Alam state television network quoted an unnamed source as saying on Sunday.
The state news agency IRNA and the semi-official Fars news agency reported that the plane is now in the possession of Iran's armed forces. The Fars news agency is close to the powerful Revolutionary Guard.
Fars reported that the drone had been brought down through a combined effort by Iran's armed forces, air defence forces and its electronic warfare unit after the plane briefly violated the country's airspace at its eastern border.
The drone "was downed with slight damage. It is now under the control of our forces," Fars reported, quoting an unnamed military source.
The source warned that Iran's armed response would "not be limited to our country's borders" for the "blatant territorial violation".
Al Alam state television network reported the same news on Sunday.
Other 'downed drones'
Trita Parsi, president of the National Iranian American Council, told Al Jazeera that Iran has made similar claims even as recently as July.
"It could be quite feasible but we don’t know yet. What we do know is that in the absence of any diplomatic channels, incidents like this can have tremendous repercussions. Far greater then when there were some de-escalatory mechanisms in place between the United States and Iran."
In January, Iran also announced that its forces had downed two US drones after they violated Iranian-controlled airspace.
It said it would put the aircraft on display to the public, but there has been no indication it ever did so.
In June, Brigadier General Amir-Ali Hajizadeh, the commander of the Guards' aerospace unit, said Iran had shown Russian experts the US drones in its possession.
"Russian experts requested to see these drones and they looked at both the downed drones and the models made by the Guards through reverse engineering," he said.
Hajizadeh did not specify how many US drones were shown nor gave any details of the copies Iran was said to have made of the aircraft.
The US military and the CIA routinely use drones to monitor military activity in the region.
They have also reportedly used them to launch missile strikes in Yemen as well as in Afghanistan and in Pakistan's lawless tribal belt.
Iran holds frequent military drills, primarily to assert an ability to defend against a potential US or Israeli attack on its nuclear facilities.
Iran is locked in a dispute with the US and its allies over Tehran's disputed nuclear programme, which the West believes is aimed at the development of nuclear weapons. Iran denies the accusations, saying its programme is entirely peaceful.