Abu Yahya al Libi, one of al Qaeda's top strategists and seen as the most prominent figure in the network after leader Ayman al Zawahri, has been killed in a drone strike in Pakistan, Pakistani intelligence officials said yesterday.

His death is the biggest blow to al Qaeda since US special forces killed Osama bin Laden in a secret raid in Pakistan in May 2011.

US sources said Libi, a Libyan cleric with a degree in chemistry who has survived previous attacks by drone aircraft, was a target of a strike early on Monday in north-west Pakistan's North Waziristan tribal region, home to some of the world's most notorious militant groups.

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.

"Libi has also been at the centre of al Qaeda's plans to reconstitute itself and try to remount a transnational terror campaign," he said.

Some US officials describe Libi, whose real name is Mohamed Hassan Qaid, as number two to Zawahri, the former Egyptian doctor who took over al Qaeda after bin Laden's death.

One US official said Libi "was among al Qaeda's most experienced and versatile leaders" and that he "played a critical role in the group's planning against the West, providing oversight of the external operations efforts",

Pakistani intelligence officials said Libi, which means Libyan in Arabic, was among seven foreign militants killed by a drone aircraft.

One said: "We intercepted some conversations between militants. They were talking about the death of a 'sheikh'. They did not name this person but we have checked with our sources and believe they are referring to Libi."