U.S. investigators probing al-Qaida terrorist facilities in Afghanistan have uncovered instructions for making chemical and biological weapons, but no evidence that such weapons were actually built.

Marine General Peter Pace says investigators are now examining some 50 sites where al-Qaida was suspected of working on so-called weapons of mass destruction - description that covers chemical, biological, or even nuclear weapons.

The general, who is vice chairman of the military's Joint Chiefs of Staff, calls the process as painstaking as the cave searches now under way in the Tora Bora region.

But he tells reporters that so far no hard evidence has been found of any actual chemical or biological weapons. General Pace said, "There have been a couple of locations where we have found documentation that is the chemistry set equivalent of this is how you make a bomb in your basement. But the documentation on how to do that is not linked with any physical evidence that in fact that occurred in that particular location so that is what we have right now."

The disclosure coincides with the revelation by Deputy Defense Secretary Paul Wolfowitz that U.S. officials are seeking information from freshly taken al-Qaida prisoners about a possible continued terrorist presence in the United States.

He calls the interrogations a top priority. Mr. Wolfowitz said, "The first priority is to get information from them, first and foremost information that can lead us to the capture of other terrorists, and I would say in particular the capture of terrorists here in the United States or other places where they might be planning operations."

But Mr. Wolfowitz calls it a complicated business and says some of the prisoners are skilled liars.

The Pentagon says the U.S. military is taking custody of more than a dozen additional captives seized by Afghan groups. It is holding five detainees on a ship in the Arabian Sea. One is an American and a second is Australian.

The other three are Taleban or al-Qaida figures who Mr. Wolfowitz says may be senior personnel. "We think we know who they are," he said, "and if they are who we think they are they are fairly important people. But one of the reasons not to start identifying them yet is we are not sure their comrades necessarily know that we have them."

But al-Qaida leader Osama bin Laden apparently remains at large. Mr. Wolfowitz says interrogations of prisoners have yielded no reliable information on his whereabouts.

Mr. Wolfowitz is warning other countries not to give the terrorist leader sanctuary, saying any country that would knowingly harbor bin Laden, in his words, would have to be out of its mind.