Surveillance drones have been widely used by Nato in Afghanistan
The Pakistani army is investigating the wreckage of a suspected US spy plane found near the Afghan border, but has rejected claims it was shot down.
A military spokesman told the BBC that the drone was recovered on Tuesday in the South Waziristan tribal area and the wreckage was being examined.
The spokesman said the crash appeared to have been due to a malfunction.
The US military has confirmed a drone crashed but said it occurred in eastern Afghanistan due to engine failure.
US Army Captain Christian Patterson told the Reuters news agency that the unmanned aerial vehicle (UAV) was being operated by US armed forces when it crashed.
"It was recovered immediately after it went down," he said. "It wasn't close to the border."
Meanwhile, fighting between Pakistani troops and Taleban militants is continuing in the tribal region of Bajaur.
In Quetta, capital of south-western Balochistan province, a young girl was killed in a suicide bombing.
About a dozen military personnel were also injured in the assault on an army vehicle.
The drone found on the Pakistani side of the border was discovered in the Zohba mountain range in Waziristan, a Taleban and al-Qaeda stronghold.
Locals living in a village at the foot of the range say they were looking for wood on the mountainside when they came across the plane.
"It was rather small for a plane," one villager told the BBC, adding: "It couldn't be more than 10 feet long."
Locals say five men carried the drone down off the mountainside and informed the army. Soldiers then took the aircraft away, as well as other debris from the site where it had crashed.
"A surveillance UAV, while flying over the Pak-Afghan border yesterday [Tuesday] night, crash-landed on this side of the border... apparently due to malfunctioning," a Pakistani military spokesman said.
"The wreckage of the UAV has been recovered from the site by the security forces personnel and the matter is under detailed investigation," the spokesman said in a statement.
The statement did not say who the drone belonged to, but security officials said they were in no doubt it was an American aircraft.
The BBC's Dilawar Khan says this is the second such crash in the region in recent years. Two years ago, a similar drone crashed near the town of Miranshah in North Waziristan.
The latest crash comes amid recent reports that Pakistani troops have opened fire to prevent the US forces from operating inside Pakistan.
"No firing was heard in the area so there is no question of it being shot down," a senior Pakistani security official told AFP.
Tensions in the border region are rising
But some residents gave a different account.
"The tribesmen fired at the drone and it fell out of the sky," one unnamed resident told AFP.
US President George Bush said on Tuesday that he wanted to help Pakistan protect itself.
He was speaking moments before his first meeting with Pakistani President Asif Ali Zardari at the sidelines of the UN General Assembly in New York.
Mr Bush did not refer directly to the controversial US strikes in Pakistan that have caused bilateral tensions.
There is growing anger in Pakistan at the US forces in Afghanistan violating Pakistani sovereignty.