The Al Qaeda trained between 70,000 and 120,000 terrorists in Afghanistan before the coalition invasion in 2002, The Independent on Sunday quoted American officials as saying.
The figure, based on testimony by senior US intelligence officials to a joint inquiry by the US Senate and House of Representatives intelligence committees, is at least three times higher than previous estimates.
The hearings were told that the Al Qaeda recruits came from more than 70 countries and were trained in making bombs, using weapons and foreign languages. Many are believed to have escaped capture and are lying low around the world.
One of the authors of the report, Senator Bob Graham, said the estimate suggests that the Al Qaeda remains the main threat to the West. The Bush administration 'lost focus' when it turned its attention to Iraq, in his view.
"We allowed Al Qaeda to regroup and regenerate," Senator Graham said.
"They've conducted a series of very sophisticated operations, thus far none in the United States, but seven Americans were killed in Saudi Arabia. We have to assume that as those people were placed around the world, some were placed inside the US. Some of them are in the US today."