But despite objections from some senators a crucial 28 pages of the 900-page report, which criticises Saudi Arabia for its lack of interest in clamping down on Islamist extremists, has been removed from the final document.

Saudi Arabia was home to 15 of the 19 hijackers yet remains a close and important ally of America in the region. The omission of criticism of Saudi Arabia was condemned by the Democratic senator and presidential hopeful, Bob Graham, a former chairman of the joint house and Senate intelligence committee.

"I start from the premise that in a democracy, the people should know as much as the government knows unless there is a very compelling case that the information threatens American security interests," he said.

The report details a breakdown in communication between various sections of the US intelligence community, but concludes that no single piece of intelligence or information could have stopped the attacks.

The inquiry comes at a sensitive time for the US intelligence community, with the Bush administration's credibility undermined by errors in the president's state of the union speech and the failure to find weapons of mass destruction in Iraq.

The report of the joint intelligence committee concludes that none of the intelligence agencies, including the FBI and CIA, had information that would have provided specific advance warning of the attacks.

The report shows that during the summer of 2000 an FBI informant was in San Diego with Khalid Almihdhar and Nawaf Alhazmi, both of whom were aboard the plane which crashed into the Pentagon. He passed their first names on to his FBI handler but they were not under suspicion as neither was on a watchlist for suspected terrorists.

The CIA knew both men had attended a meeting of al-Qaida operatives in Malaysia several months earlier but did not pass the information on to the FBI. It was not until August 23 2001, just weeks before the attacks, that the men's names were placed on lists of suspected terrorists.

But when the CIA finally warned the FBI, giving information including the men's full names, FBI officials in Washington sent the names only to the bureau's counterterrorism offices in New York and Los Angeles, neither of which passed the information to San Diego. The full names were not passed on to agents in San Diego until hours after the attacks on September 11, when they were identified from passenger lists.

The report also details the role played in San Diego by Omar al-Bayoumi, a student with links to officials at the Saudi Arabian consulate in Los Angeles. He met Almidhar and Alhazmi in LA. The report says a reliable FBI source had told US agents that Bayoumi "must have been an intelligence officer for Saudi Arabia or another foreign power". He has now left the country for Saudi Arabia.