Al-Qaeda confirmed on Islamist websites Sunday that its chemical and biological weapons expert, Abu Khabab al-Masri, had been killed in a US airstrike on a Taliban hide-out in Pakistan.

Three other al-Qaeda members and an unnamed number of children were killed in the airstrike on July 28.

Al-Masri, also known as Midhat Mursi, is believed to have headed al-Qaeda's weapons-of-mass-destruction programme under the code name al-Zabadi (curdled milk).

He is believed to have planned a thwarted chemical attack on the Jordanian capital Amman in 2004.

Even before the fundamentalist Taliban regime was driven out of Afghanistan by the US and its allies following the September 11, 2001, attacks on New York and Washington DC, al-Masri was employed as al-Qaeda's instructor for unconventional warfare.

In Afghanistan, the Egyptian-born terrorist carried out poison-gas experiments on dogs.

He wrote several manuals on how to produce and use improvised chemical and biological weapons. Washington placed a 5-million-dollar bounty on his head.

Experts say his death will be a major blow to the international terrorist network and its ability to strike. US missiles destroyed a Koran school in Pakistan's semi-autonomous tribal region of North Waziristan on July 28. Pakistani authorities initially said that six people had died in the attack: three foreign extremists and three local boys.

It was already suspected at the time that al-Masri was among the dead.