WASHINGTON  —  Al Qaeda (search) had progressed much further toward developing a particular biological weapon before the Sept. 11 attacks than the United States realized, the presidential commission investigating intelligence on weapons of mass destruction (search) found.

The intelligence community was surprised by Al Qaeda's advances in a virulent strain in the disease, identified by the commission only as "Agent X" (search) to prevent Al Qaeda from knowing what the U.S. government has learned.

The discovery of Al Qaeda's work came only after the U.S.-led war in Afghanistan removed the Taliban from power, the report says.

"Al Qaeda's biological program was further along, particularly with regard to Agent X, than pre-war intelligence indicated," the report says. "The program was extensive, well-organized, and operated for two years before September 11, but intelligence insights into the program were limited."

It was not so advanced that Al Qaeda had a functioning weapon, the report says.

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U.S. officials have previously said they found signs of Al Qaeda's work in anthrax (search) weapons in Afghanistan, but it was not clear if "Agent X" referred to anthrax. Other diseases that may be turned into weapons include smallpox, plague and ebola.

The work on Agent X was done at several sites in Afghanistan, including two with commercial lab equipment. Some intelligence information suggests cultures of the disease had been isolated and basic production was possible, the report says, but notes this is uncertain information.

U.S. assessments of Al Qaeda's other efforts to acquire a weapon of mass destruction did not change substantially after U.S. and Afghan forces removed the Taliban from power after the Sept. 11 attacks, the report says. Al Qaeda was studying nuclear weapons and contacted Pakistani scientists to discuss nuclear weapons, it notes.

"We found that just prior to the war in Afghanistan in 2001, the Intelligence Community was able to correctly assess Al Qaeda's limited ability to use unconventional weapons to inflict mass casualties," the report says. "Yet when the war uncovered new evidence of WMD efforts, analysts were surprised by the intentions and level of research and development underway by al-Qaida. Had this new information not been acquired, and had Al Qaeda been allowed to continue weapons development, a future intelligence failure could have been in the offing."