A U.S. drone fired a missile at a Taliban vehicle in Pakistan's North Waziristan ethnic Pashtun tribal region on the Afghan border on Monday, killing at least four militants, Pakistani intelligence officials and residents said.

Pakistani Taliban chief Baitullah Mehsud was killed in a similar attack in the neighboring South Waziristan region, on August 5.

The U.S. Central Intelligence Agency operates the missile-firing Predator and Reaper drones. Here are some key facts and responses to questions raised by the strikes:

WHY DOES THE UNITED STATES ATTACK?

Many al Qaeda and Taliban members 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 56 drone air strikes since the start of 2008, killing about 500, including many foreign militants, according to reports from Pakistani intelligence agents, district government officials and residents.

U.S. attacks on Pakistani Taliban leader Mehsud and his men 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 U.S. lawmaker, Senator Dianne Feinstein, told a U.S. Senate hearing in February that the drones were being flown from an air base inside Pakistan. Pakistan denied that, saying it had never granted permission for the strikes.

WHAT IS PAKISTAN'S POSITION?

Pakistan officially objects to the U.S. drone strikes, saying they violate its sovereignty. It also worries the strikes could undermine efforts to deal with militancy because the civilian casualties 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.

WHAT IS THE U.S. POSITION?

The United States says the missile strikes are carried out under an agreement with Islamabad that allows Pakistani leaders to decry the attacks in public. U.S. officials said in May that Washington had given Pakistan data on militants gathered by surveillance drones in Pakistani airspace under an agreement with Islamabad.

WHO WERE THE MOST PROMINENT MILITANTS PEOPLE REPORTED

KILLED?

January 28, 2008 - A senior al Qaeda member, Abu Laith al-Libi.
July 28 - An al Qaeda chemical and biological weapons expert, Abu Khabab al-Masri.

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. An Egyptian named as Abu Zubair al-Masri was also reported killed.

January 1, 2009 - Pakistani agents said a drone killed three foreign fighters. A week later, a U.S. counter-terrorism official said al Qaeda's operational chief, Usama al-Kini, and an aide had been killed. The U.S. official declined to give any details.

August 5 - U.S. drones fired missiles into Baitullah Mehsud's father-in-law's house. Pakistani and U.S. officials said Mehsud was killed in the strike, while Taliban said he had been seriously wounded and died days later.

(Compiled by Islamabad Newsroom; Editing by Tomasz Janowski)

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