FACTBOX: U.S. drone strikes in Pakistan

By Augustine Anthony

ISLAMABAD (Reuters) - Suspected U.S. drone aircraft fired missiles at militant targets in Pakistan's South Waziristan tribal region on the Afghan border on Thursday, killing at least five people, intelligence officials said.

Civilian casualties caused by the missile-carrying, pilotless drones, operated by the U.S. Central Intelligence Agency, have infuriated many Pakistanis and made it harder for the government to cooperate with the United States.

Here are some facts about the U.S. 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 ATTACK?

Many al Qaeda members and Taliban fled to northwestern Pakistan's ungoverned ethnic Pashtun belt after U.S.-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 40 drone air strikes since the beginning of last year, most since September, killing more than 335 people, including many foreign militants, according to a tally of reports from Pakistani intelligence agents, district government officials and residents. There have been 19 attacks this year.

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.

October 31 - A mid-level al Qaeda leader, Abu Akash, was killed in an attack in North Waziristan.

November 19 - An Arab al Qaeda operative identified as Abdullah Azam al-Saudi was killed in Bannu district.

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 to be among the dead in the same attack.

January 1, 2009 - A U.S. drone killed three foreign fighters in South Waziristan, Pakistani agents said. A week later, a U.S. counter-terrorism official said al Qaeda's operational chief Usama al-Kini and an aide had been killed in South Waziristan. The U.S. official declined to say how or when they died.

WHERE ARE THE DRONES LAUNCHED FROM?