A secret U.S. surveillance drone that went missing last week in western Afghanistan appears to have crashed in Iran, in what may be the first case of such an aircraft ending up in the hands of an adversary.

Iran’s news agencies asserted that the nation’s defense forces brought down the drone, which the Iranian reports said was an RQ-170 stealth aircraft. It is designed to penetrate enemy air defenses that could see and possibly shoot down less-sophisticated Predator and Reaper drones.

A stealthy RQ-170 drone played a critical role in surveilling the compound in Pakistan where Osama bin Laden was hiding in the months before the raid in which he was killed by U.S. Navy SEALs in May.

U.S. officials acknowledged Sunday that a drone had been lost near the Iranian border, but they declined to say what kind of aircraft was missing.

The Iranian government has not released any pictures of the recovered aircraft, which they said was downed by defense forces after it flew across the border and into the country’s airspace. An unnamed Iranian defense official said in one report that a cyber­attack caused the drone to crash.

U.S. officials cast doubt on this and other Iranian assertions. “We have no indication that it was brought down by hostile fire,” said a senior Pentagon official, speaking on the condition of anonymity to discuss sensitive surveillance activity.

If an RQ-170 drone crashed in Iran, it would mark a significant setback for the U.S. military. The United States has lost less-sophisticated unmanned aircraft in recent years over Iran, but a nearly intact RQ-170 could offer a potential windfall of useful intelligence for the Iranians and their allies.

The aircraft has special coatings and a batwing-like shape that is designed to evade detection by enemy radar. The aircraft could help the Iranians better understand the vulnerabilities of U.S. stealth technology and provide them with clues on how to spot other aircraft, U.S. officials said.

Similar stealth technology is used in U.S. B-2 bombers and is a major feature of the military’s F-35 fighter jet, which is one of the largest and most expensive weapons programs in Pentagon history.

The first reports of the drone crash came from Iran’s semiofficial Fars News Agency. “Iran’s army has downed an intruding RQ-170 American drone in eastern Iran,” the Arabic-language al-Alam state television network quoted an unnamed source as saying. “The spy drone, which has been downed with little damage, was seized by the armed forces.”

Hours after the incident, Iranian state TV news was showing only stock pictures of RQ-170 stealth drones, not images from the crash. An unnamed military official told the Fars News Agency that Iran’s response “will not be limited to the country’s borders.”

The U.S. military released a short statement later Sunday on the missing drone. “The [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,” it said. “The operators of the UAV lost control of the aircraft and had been working to determine its status.”

The Air Force first acknowledged that it was flying stealth drones in 2009, after an RQ-170, which is made by Lockheed Martin, was spotted and photographed at the main U.S. airfield in Kandahar, Afghanistan.

The CIA used an RQ-170, which flies at high altitudes to evade enemy air defenses, to make repeated secret flights into Pakistan this year and capture surveillance video of the walled compound where bin Laden was hiding.

Stealth drones also were used on the night of the raid to provide the imagery that President Obama and members of his national security team watched. In addition to providing video, the drones can eavesdrop on radio transmissions. They have become a critical surveillance tool for U.S. officials in the Middle East and Central Asia.

It is not clear what might have caused the drone’s remote pilots to lose control of the aircraft as it flew near the Iranian border. The statement by the Iranian news agency that the surveillance drone had been recovered with “little damage” seemed to cast doubt on the assertions that it had been shot out of the sky.

“If this happened, it is a 95 percent chance that it just malfunctioned,” said a second senior Pentagon official, also speaking on the condition of anonymity. “There are a lot of things that can fail.”

In the past, pilots have lost satellite connections to drones, causing them to veer off course, run out of fuel and crash. It is also possible that the aircraft suffered other mechanical problems.

U.S. officials brushed off claims about a cyberattack downing the drone as preposterous.

Such attacks are very difficult to execute, especially with the latest generations of aircraft, which use encrypted satellite technology that is very hard for ground systems to intercept and modify, said cyber experts. Even if an enemy could somehow breach the satellite communications, only the most sophisticated adversary could crack the encryption protecting control codes, experts said.

U.S. officials declined to comment on what the drone’s mission had been before it crashed. The U.S. military flies surveillance drones along Afghanistan’s border with Iran to try to spot militants moving into the country.

A stealth drone, even if it stayed on the Afghan side of the border, could peer several miles into Iran without being detected by Iranian radar and provide useful intelligence about troop movements or insurgent activity in the country.

U.S. military officials, however, have said in recent years that they have not seen a major influx of fighters or weaponry into Afghanistan from Iran. By contrast, the U.S. military has complained loudly and frequently about Iranian interference and support for militias in Iraq.

The incident with the drone follows a week of heightened tensions between Iran and the West after young Iranian hard-liners stormed the British Embassy compound and a separate diplomatic residence in Tehran on Tuesday. Britain pulled its diplomatic staff from the Islamic republic after the attack and ordered Iran’s diplomats to leave London. The Iranian delegation arrived in Tehran on Saturday.

In July, Iran also claimed to have shot down a U.S. spy drone, which U.S. officials denied. Iran’s Revolutionary Guard later backed away from the claim, saying its air defenses had hit only a test target.

Erdbrink reported from Tehran. Staff writers Ellen Nakashima and Greg Miller in Washington contributed to this report.