It has been revealed that the US Federal Aviation Administration received 52 intelligence reports ahead of 11 September 2001 that al-Qaeda intended to attack airlines in the United States.
The information is contained in a recently declassified report by the commission that was set up to investigate the 11 September attacks.
The commission found that the administration had been given the warnings between April and September 2001.
In its judgement, the commission said that the FAA had been lulled into a false sense of security.
A spokesman for the administration said intelligence was passed on to airlines and airports but none of it was specific enough to allow the attacks to be prevented.
