A senior U.S. defense official says the Pentagon believes the al-Qaida terrorist network has chemical weapons and possibly biological ones.

A senior U.S. defense official refuses to discuss whether the al-Qaida facilities now being targeted by American forces in Afghanistan include sites where the terrorists may store weapons of mass destruction.

But the official, speaking on condition of anonymity, says the Pentagon believes the terrorist organization does have what he terms a "crude" chemical weapons capability, and possibly a biological weapons capability as well.

The official tells reporters at the Pentagon that if al-Qaida has a nuclear capability, it is liable to be more radiological than fissile - that is a capability to spread potentially dangerous radiation but not to trigger an actual nuclear explosion.

He says al-Qaida's chemical capability involves poisonous gases such as chlorine and phosgene.

In the biological weapons area, he says the terrorist group may have toxins, possibly anthrax.

He declines to discuss possible quantities the terrorists might have - whether, as he puts it, it amounts to a bucket-full or a ton.

He says al-Qaida may have what he terms innovative but probably not sophisticated delivery means. He notes news reports of terrorist suspects in the United States examining crop duster aircraft or the use of hand sprayers.

In another development, the official says the Pentagon believes there have been defections of Taleban forces to the opposition since U.S. air-strikes began. He describes these has a significant sign of Taleban instability.

But the official could not confirm opposition claims that the defectors include 40 commanders and 1,200 Taleban fighters.