It contained medical supplies and commonly available laboratory equipment suitable for growing biological samples as well as a variety of associated supplies

Air Force Major Bill Harrison

"US special forces operating in the vicinity of Kandahar found a possible al-Qaeda chemical and biological research facility," Central Command spokesman Lieutenant Commander Matthew Klee said.

The laboratory in Afghanistan was believed to still be under construction when it was abandoned and there was no evidence of any chemical or biological weapons having been made there.

However, the US military still believes it is possible that the facility was intended for the manufacture of weapons.

Five people died in the anthrax attacks last autumn

"It contained some laboratory equipment and possibly was intended for use in a biological warfare production effort," Mr Klee said.

Mr Klee added that the facility could have been used for the manufacture of "just about any kind" of biological weapon.

Air Force Major Bill Harrison, a spokesman for the military's Central Command, said "it contained medical supplies and commonly available laboratory equipment suitable for growing biological samples as well as a variety of associated supplies".

The US has long contended that the al-Qaeda group led by Osama bin Laden was trying to acquire biological and chemical weapons and this may be the strongest indication yet.

'No hijacker link'

Meanwhile the FBI says it has found no evidence linking the hijackers who carried out the 11 September attacks with a subsequent series of anthrax attacks.

Five people died from anthrax in the US after handling letters in the weeks following the attacks, and there were suspicions that the events might be connected.

However, the Assistant FBI Director, John Collingwood, said this possible link had been fully investigated, and exhaustive testing had not shown that anthrax was present anywhere the hijackers had been.

Leg lesion

Mr Collingwood's statement followed reports that one alleged hijacker had been treated for a lesion consistent with anthrax last June.

According to a report in The New York Times Ahmed Alhaznawi had received treatment from a Florida doctor for a dark lesion on his leg.

At the time the doctor had no thought of anthrax being a cause as it was extremely rare in the US and unfamiliar to most doctors.

But following the anthrax attacks in America the doctor reviewed his medical notes and concluded that the lesion could have been consistent with anthrax.

But Mr Collingwood said the government had carefully looked at the case. "This was fully vetted among multiple agencies several months ago," he said.

The FBI says investigators have still not identified where the anthrax which led to the five deaths came from.