Iranian TV has shown the first video footage of an advanced US drone aircraft that Tehran says it downed 140 miles (225km) from the Afghan border.
Images show Iranian military officials inspecting the RQ-170 Sentinel stealth aircraft which appears to be undamaged.
US officials have acknowledged the loss of the unmanned plane, saying it had malfunctioned.
However, Iranian officials say its forces electronically hijacked the drone and steered it to the ground.
BBC security correspondent Frank Gardner says the intact condition of the Sentinel tends to support their claim.
Iran's Press TV said that the Iranian army's "electronic warfare unit" brought down the drone on 4 December as it was flying over the city of Kashmar.
Brig General Amir-Ali Hajizadeh, head of Iran's Revolutionary Guards' aerospace unit, told Iranian media that the drone "fell into the trap" of the unit "who then managed to land it with minimum damage".
He said Iran was "well aware of what priceless technological information" could be gleaned from the aircraft.
Nato said at the weekend that an unarmed reconnaissance aircraft had been flying a mission over western Afghanistan late last week when its operators lost control of it.
Pentagon officials have said they are concerned about Iran possibly acquiring information about the technology.
Iranian media said on Thursday that the foreign ministry had summoned the Swiss envoy to express its "strongest protest over the invasion of a US spy drone deep into its airspace".
Washington has no diplomatic relations with Iran and US affairs in the country are dealt with via the Swiss embassy in Tehran.
TEHRAN (Reuters) - Iranian media reported on Sunday that their country's military had shot down a U.S. reconnaissance drone in eastern Iran, but a U.S. official said there was no indication the aircraft had been shot down.
NATO's U.S.-led mission in neighbouring Afghanistan said the Iranian report could refer to an unarmed U.S. spy drone that went missing there last week.
The incident comes at a time when Tehran is trying to contain foreign outrage at the storming of the British embassy on Tuesday, after London announced sanctions on Iran's central bank in connection with Iran's nuclear enrichment programme.
Iran has announced several times in the past that it shot down U.S., Israeli or British drones, in incidents that did not provoke high-profile responses.
"Iran's military has downed an intruding RQ-170 American drone in eastern Iran," Iran's Arabic-language Al Alam state television network quoted a military source as saying.
"The spy drone, which has been downed with little damage, was seized by the Iranian armed forces," the source said. "The Iranian military's response to the American spy drone's violation of our airspace will not be limited to Iran's borders."
Iranian officials were not available to comment further.
NATO's International Security Assistance Force in Afghanistan said in a statement: "The UAV (unmanned aerial vehicle) to which the Iranians are referring may be a U.S. 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."
A U.S. official, who asked not to be named, said: "There is absolutely no indication up to this point that Iranians shot down this drone."
In January Iran said it shot down two unmanned Western reconnaissance drones in the Gulf. In July Iran said it had shot down an unmanned U.S. spy plane over the holy city of Qom, near its Fordu nuclear site.
(Additional reporting by Ramin Mostafavi in Tehran, Caren Bohan and David Alexander in Washington and Missy Ryan in Bonn; Writing by Parisa Hafezi; Editing by Peter Graff)