The 10-member bipartisan commission probing the 9/11 attacks in the United States has criticised the Central Intelligence Agency and Federal Bureau of Investigation for their failure to recognise the Al-Qaeda threat despite several warnings.

The agencies had recognised the Al-Qaeda's emergence more than a decade after it was founded in 1988, playing down reports that documented the danger posed by the group, a report released by the commission said on Friday.

The CIA's Counter Terrorist Centre never developed a plan to deal with the possibility that terrorists might use airplanes as weapons, despite growing evidence during the 1990s that terrorist groups had attempted or were planning such plots, the report said.

CIA Director George J Tenet acknowledged that he did not brief President George W Bush, FBI officers or cabinet members after he was informed in late August 2001 of the arrest of Zacarias Moussaoui, who was later charged as a conspirator in the attacks.

Nor did he mention the case at a September 4, 2001 White House cabinet meeting, where approval was given for a new presidential directive on terrorism. The briefing for Tenet was titled 'Islamic Extremist Learns to Fly'.

Referring to the failure to detect the terror plot that left more than 3,000 people dead, Tenet told the panel, "We all understood bin Laden's intent to strike the homeland but were unable to translate this knowledge into an effective defence of the country."

He also said it would take five more years to "have the kind of clandestine service our country needs".

The commission also found that major collection and analysis activities targeting the Al-Qaeda were delayed even after a defector from the organisation began providing details about the network in 1996.

The CIA had learned that Osama bin Laden was linked to the 1992 attacks on US military personnel in Yemen and the 1993 downing of a US Army Black Hawk helicopter in Somalia, the report added.

The agency also received reports in 1997 that Al-Qaeda operatives were checking out institutions in the US as a precursor to an attack. But still the American intelligence community "did not describe this organisation, at least in documents we have seen, until 1999", the report said.

In one of its more stinging case studies, the report noted that Tenet had learnt about the arrest of a suspected militant who was attempting to learn how to fly jetliners in Minnesota on August 23 or 24, 2001, a week earlier of Moussaoui.

In fact, the Moussaoui information remained in the FBI's international terrorism division until a week before the attacks. Thomas J Pickard, acting FBI director, has testified that he did not learn of it until the afternoon of September 11, 2001.