"Let's see what the chemicals are," Blix told a packed gathering of the Oxford Union debating club, after Iraqi officials claimed to have uncovered a chemical bomb factory in Fallujah.

"Many of these stories evaporate when they are looked at more closely," he told the mainly student crowd. "If there were to be found something, we would all be surprised."

He added: "The chances (that the laboratory could produce weapons) are, I think, relatively small. I would be surprised if it was something real."

Iraq's national security chief Kassen Daoud said Iraqi national guardsmen fighting alongside US forces in Fallujah had found a "chemical materials laboratory that was used to make explosives and toxic substances".

Pamphlets showing how to make explosives and toxic substances, including anthrax, were also found, added Daoud, who was speaking Thursday in Baghdad.

Blix, a former Swedish diplomat, was charged with searching for weapons of mass destruction in the 15 weeks leading up to the US-led invasion of Iraq last year.

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