U.S.investigators have found trace evidence of anthrax and another deadly poison at several suspected al-Qaida terrorist facilities in Afghanistan.

Top Pentagon officials say there is no conclusive evidence that al-Qaida developed the capability to manufacture large quantities of anthrax, or other chemical or biological weapons.

But General Richard Myers, chairman of the joint chiefs of staff of the U.S. armed forces, says investigators have found a laboratory in Kandahar with equipment indicating an interest in making anthrax.

General Myers also discloses that, at several sites, investigators have turned up positive traces of anthrax and ricin, which comes from the castor bean plant, and is regarded as one of the most poisonous naturally occurring substances known. "In sites we have exploited so far, I think in five or six cases, some of the swabs we took have turned out positive for anthrax and, I think, ricin," he said.

Still, General Myers says the amounts were so insignificant they could be naturally-occurring. "But the caveat to that is that they're such minute amounts, that the anthrax could be naturally occurring, and the ricin could be there because of the castor bean," said General Myers. "It could be that, and, so, no conclusive proof of active agents."

Nevertheless, General Myers and Defense Secretary Donald Rumsfeld say there is plenty of evidence of al-Qaida's interest in developing chemical and biological weapons capabilities.