Pakistani Taliban chief Baitullah Mehsud was probably killed in a missile attack on Wednesday, the country's interior minister said on Friday.
The attack, in Mehsud's stronghold in the tribal region of South Waziristan near the Afghan border, is believed to have been carried out by a pilotless US drone aircraft.
Here are some facts about the US missile attacks, the controversy they have caused, and a list of some of the more prominent militants killed, according to Pakistani officials.
Why does the United States carries out drone attacks?
Many al Qaeda members and Taliban fled to northwestern Pakistan's ungoverned ethnic Pashtun belt after US-led soldiers ousted Afghanistan's Taliban government in 2001. From their sanctuaries there, the militants have orchestrated insurgencies in Afghanistan and Pakistan.
The United States and Afghanistan have pressed Pakistan to eliminate the sanctuaries. Apparently frustrated by Pakistan's inability to do so, the United States is hitting the militants itself.
How many attacks?
The United States has carried out about 50 drone air strikes since the beginning of last year, most since September. The death toll stands at about 480 people, including many foreign militants, according to a tally of reports from Pakistani intelligence agents, district government officials and residents.
US attacks on Mehsud territory in South Waziristan picked up after the Pakistani government ordered a military offensive against him in June.
Where are the drones launched from?
A senior US lawmaker, Senator Dianne Feinstein, told a US Senate hearing in February that drones were being operated and flown from an air base inside Pakistan. Pakistan denied that, saying no permission had ever been issued for the strikes.
Although its military has also bombarded Mehsud's stronghold with air raids and artillery, Pakistan officially objects to the US drone strikes, saying they violate its sovereignty.
Pakistan also worries the strikes could undermine efforts to deal with militancy because the civilian casualties they cause inflame public anger and bolster support for the fighters.
Pakistan has pressed the United States to provide it with drones to allow it to conduct its own anti-militant operations.
The United States has shrugged off Pakistani protests. It says the missile strikes are carried out under an agreement with Islamabad that allows Pakistani leaders to decry the attacks in public.
US officials said in May that Washington had given Pakistan data on militants in the Afghan border area gathered by surveillance drones in Pakistani airspace under an agreement with Pakistan.
Some of the people reported killed:
January 28, 2008: A senior al Qaeda member, Abu Laith al-Libi, was killed in a strike in North Waziristan.
July 28: An al Qaeda chemical and biological weapons expert, Abu Khabab al-Masri, was killed in South Waziristan.
November 22: Rashid Rauf, a Briton with al Qaeda links and the suspected ringleader of a 2006 plot to blow up airliners over the Atlantic, was killed in an attack in North Waziristan. An Egyptian named as Abu Zubair al-Masri was said also to be killed.
January 1, 2009: A US drone killed three foreign fighters in South Waziristan, Pakistani agents said. A week later, a US counter-terrorism official said al Qaeda's operational chief, Usama al-Kini, and an aide had been killed in South Waziristan. The US official declined to say how or when they died.