Drones can be remotely controlled from thousands of miles away
Four missiles fired by a US drone aircraft in the northern Pakistani tribal region of North Waziristan have killed three militants, officials say.
They say that a militant camp was also destroyed by the missiles.
Separately Pakistani intelligence officials say US drone missiles recently killed a militant on the FBI's most-wanted terrorists list.
The man, named as Jamal Saeed Abdul Rahim, is believed to have died on 9 January in North Waziristan.
The FBI's Web site says that Mr Rahim has a $5m bounty on his head and is wanted for his alleged role in the 1986 hijacking of Pan American World Airways flight during a stop in the southern Pakistani city of Karachi.
More than 700 people have been killed in about 77 US drone strikes since August 2008.
A surge in such strikes has been ordered by US President Barack Obama, with seven drones hitting the tribal north-west this month alone.
The US has stepped up the number of drone attacks since 30 December, when a suicide bomber killed seven Central Intelligence Agency (CIA) employees over the border in Afghanistan.
The Pakistani Taliban denied on Thursday their leader, Hakimullah Mehsud, was killed in a US missile attack in the north-west.
A Taliban spokesman told the BBC that Hakimullah Mehsud was wounded in the attack but his injuries were not serious.
North and South Waziristan - where the Mehsud faction comes from - are major sanctuaries for al-Qaeda and Taliban militants.
Pakistan's army launched an offensive in South Waziristan in October and is under US pressure to do the same in North Waziristan.
Pakistan has publicly criticised drone attacks, saying they fuel support for the militants. But observers say that the authorities privately condone the strikes.
The US military does not routinely confirm drone attacks, but analysts say the US armed forces and CIA in Afghanistan are the only forces capable of deploying drones in the region.