WASHINGTON/PESHAWAR - A US drone strike in Pakistan killed one of al Qaeda's most powerful figures, the US government announced 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 US 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.

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

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 US raid in which he was killed last year show Libi to have been one of a handful of al Qaeda officials relied upon by bin Laden 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 US custody in Afghanistan in 2005 and on at least one previous occasion was prematurely reported to have been killed in a US drone strike.

A Pakistani Taliban leader, speaking to Reuters by telephone from an undisclosed location, said Libi "had been living in the Mirali area for quite a while. Most of the people from his group were also in Mirali. When the first missile hit, they went to the house to check the damage."

"And immediately, another missile hit them at the spot. Unfortunately, Sheikh sahib (Libi) was martyred. This is a big loss, he was a great scholar. After doctor Sahib (Zawahri), he was the main al Qaeda leader," the Pakistani Taliban leader said.

US President Barack Obama has made strikes against anti-US militants, and particularly the killing of bin Laden, a major component of his bid for re-election in November.

Sajjan Gohel, chief executive of the Asia-Pacific Foundation security research consultancy, said Libi was one of the few remaining key figures within al Qaeda's core.      

He "has also been at the center of al Qaeda's plans to reconstitute itself and try and remount a trans-national terror campaign. This is one of the reasons he was viewed as a high value target," he told Reuters by email.