The head of an independent commission investigating the September 11 attacks yesterday said that they could and should have been prevented, and that the officials responsible for the failure should be fired.

His full report is not due to be published before May, but the comments by the commission's chairman, Thomas Kean, suggest its conclusions are likely to be politically explosive.

"This is a very, very important part of history and we've got to tell it right," Mr Kean, former Republican governor of New Jersey appointed by the Bush administration, told CBS television. "As you read the report, you're going to have a pretty clear idea what wasn't done and what should have been done... This was not something that had to happen."

... Mr Kean said the officials responsible for the intelligence failure should have been fired. So far, no one in the CIA and FBI found to have shelved repeated warnings that an attack like September 11 was being planned by al-Qaida, have suffered setbacks in their careers.

"There are people that, if I was doing the job, would certainly not be in the position they were in at that time because they failed. They simply failed," Mr Kean said.

The commission could also investigate another sensitive issue removed from the congressional report in December 2002 - the possible knowledge or role of Saudi officials in the September 11 plot.

Unheeded warnings

1995 Abdul Hakim Murad, an accomplice of Ramzi Yousef, the mastermind of the 1993 bombing of the World Trade Centre, tells Philippine authorities that he learned to fly at US flying schools as part of a plot to hijack an airliner and fly it into CIA HQ in Langley, Virginia. Philippine police inform the FBI immediately. "Murad's idea is that he will board any American commercial aircraft pretending to be an ordinary passenger, then he will hijack said aircraft, control its cockpit, and dive it at the CIA headquarters," a police report from 1995 says.

January 2000 Two future hijackers, Khalid al-Mihdhar and Nawaf al-Hazmi, are observed arriving in Kuala Lumpur for a meeting with al-Qaida suspects there. The two men then fly to California, but the CIA does not inform customs or immigration about its suspicions.

July 2001 Ken Williams, an FBI agent in Phoenix, Arizona, sends a memo to his superiors warning that Middle Eastern terrorists could be using American flying schools to train for future hijackings. The memo says the possibility has been examined by US law enforcement since April 2000. The "Phoenix memo" makes it as far as FBI HQ but no action is taken.

August 2001 As part of his morning briefing on August 6 during a "working holiday" on his Texas ranch, the president is told that al-Qaida might be planning hijackings against US targets.

August 2001 Zacarias Moussaoui is arrested in Minnesota after a flight instructor calls the FBI to voice his suspicion that the Frenchman is training to hijack a plane full of passengers. French intelligence quickly confirms Moussaoui has links with extremist groups.

FBI HQ turns down a request to search his possessions which would have revealed links to other hijackers. A Minnesota FBI official, Coleen Rowley, later issues a whistleblowing memo saying her office "identified [Moussaoui] as a terrorist threat from a very early point". On hearing about the September 11 attacks, the CIA director, George Tenet, reportedly says: "I wonder if it has anything to do with this guy taking pilot training."