FACTBOX: U.S. drone strikes in Pakistan

ISLAMABAD (Reuters) - A suspected U.S. drone strike in Pakistan's South Waziristan region killed 14 militants on Tuesday, a Pakistani intelligence agency official and residents said.

The missiles were fired in an area controlled by Pakistani Taliban leader and al Qaeda ally Baitullah Mehsud, where Pakistani troops are gearing up for an offensive.

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 45 drone air strikes since the beginning of last year, most since September, killing about 424 people, including many foreign militants, according to a tally of reports from Pakistani intelligence agents, district government officials and residents.

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 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?

A senior U.S. lawmaker, Senator Dianne Feinstein, told a U.S. Senate hearing in February that drones were being operated and flown from an air base inside Pakistan. Pakistan denied that, saying there was no permission for the strikes, nor had there ever been.

U.S. POSITION

The United States has shrugged off Pakistani protests. It says the missile strikes are carried out under an agreement with Islamabad which allows Pakistani leaders to decry the attacks in public.