Top al Qaeda strategist killed in Pakistan

(Reuters) - A U.S. drone strike in Pakistan killed one of al Qaeda's most powerful figures, the U.S. government said on Tuesday, dealing the biggest in a series of blows to the militant group since the raid that killed founder Osama bin Laden last year.

Abu Yahya al-Libi, a veteran militant said to have been a leader of the group's operations, and who survived previous U.S. attacks, was killed in the drone strike early Monday morning on a hideout in North Waziristan in Pakistan's tribal areas, officials said.

The White House called Libi's death a "major blow" to al Qaeda, and claimed that it will be hard for the group to find someone of similar stature to replace him.

Some private analysts agreed, saying that the group that launched the September 11 attacks in the United States in 2001 now faces a crisis over its future.

But even as al Qaeda's core group, now led by Ayman al-Zawahri, reels from mounting losses, its affiliates elsewhere - particularly in Yemen - have continued planning attacks on U.S. and other Western targets.

The drone strikes, which have escalated in number over the last two weeks, have deeply angered Pakistan's government and contributed to unrelenting tensions between Washington and Islamabad.

Pakistan summoned the U.S. charge d'affaires to its foreign ministry to convey "serious concerns" over the drone strikes, a ministry statement said.

For the United States, Libi had been one of al Qaeda's most dangerous figures.

Recently released letters written by bin Laden and captured during the U.S. raid in which he was killed last year show Libi was one of a handful of al Qaeda officials bin Laden relied on to argue al Qaeda's case to a worldwide audience of militants, in particular to the young.

Libi, a cleric whose real name was Mohamed Hassan Qaid, escaped from U.S. custody in Afghanistan in 2005 and on at least one previous occasion was prematurely reported to have been killed in a U.S. drone strike.