CIA infiltrated al-Qaeda before 9/11

Clarke said that in 1999, former CIA director George Tenet ordered spies to penetrate al-Qaeda for information on its leader, Osama bin Laden.

"Over the course of the subsequent three years they did go form (censored) penetrations of one sort or another, none of them very high level," Clark told members of Congress in June 2002 during closed-door testimony whose censored transcript was released this week.

"We could not conduct those military strikes to kill bin Laden, because we never knew where he was going to be in advance.

"And usually we were only informed about where he was after the fact."

Before the 2001 attacks, bin Laden had bombed two US embassies in Africa, the USS Cole in Yemen and other targets.

"By 1997 and 1998, they were operating an Afghan cell inside Afghanistan to surveil bin Laden to provide information of where he was, so that we could perhaps snatch him," Clarke said.

"Their information was never timely."

Clarke was a member of the National Security Council, which advises the president. He caused waves earlier this year by saying the Bush administration missed cues that could have prevented the 2001 attacks, which killed 3,000 people.

In August, 1998, the United States was advised several days in anticipation of bin Laden's location and launched missiles at his camp, in reprisal for the embassy bombings in Nairobi and Dar es Salam.