The US Attorney General, John Ashcroft, has said the full might of US forces would have been activated if the intelligence services had realised that al-Qaeda planned to attack mainland America.
He has been responding to the preliminary report of the commission in Washington investigating the 11 September attacks.
It has accused the FBI of failing over several years to respond to the steadily growing threat of terrorism.
Mr Ashcroft told the commission that a wall of legal restrictions prevented intelligence services from co-operating effectively.
