Abdel Bari al-Atwan, editor-in-chief of al-Quds Al Arabi newspaper, said al-Masri "represented the old guard of al-Qaeda, so it is going to be very difficult to replace him".

"This was a huge success for the Americans in their pursuit of al-Qaeda leaders," he said.

"Al-Qaeda usually replace these people in this situations, but actually, they won't have the people with the determination and expertise of this man.

"He managed to experiment a lot with chemical and biological weapons in the Tora Bora area.

"Maybe he has disciples, but there's no one with his skills. He knows the ideology of al-Qaeda very well and I don't believe he will be easily replaced by other people."

Al-Masri, a 55-year-old Egyptian chemist, was regarded as one of the group's senior bomb makers.

The statement said he had left behind him a generation of so-called students who would avenge his killing.

On Saturday, a Pakistani Taliban spokesman denied a US media report that Ayman al-Zawahri, al-Qaeda's deputy leader, had been wounded or killed in what was believed to be the same US missile strike that killed Masri.