The panel investigating the September 11, 2001, attacks has found that a "failure of imagination" kept US officials from understanding the al Qaeda threat before the attacks on New York and Washington, reports CNN and other agencies.
The final report, which comes after two years of painstaking investigations, recommends a sweeping overhaul of US intelligence services and the setting up an intelligence director to coordinate efforts.
Other measures include the creation of a national counter-terrorism center, and a "network-based information sharing system that transcends traditional governmental boundaries."
The "most important failure" leading to the 11 September attacks "was one of imagination", it says. "We do not believe leaders understood the gravity of the threat."
"The terrorist danger from [Osama] Bin Laden and al-Qaeda was not a major topic for policy debate among the public, the media, or in the Congress. Terrorism was not the overriding national security concern for the US government under either the Clinton or pre-9/11 Bush administration," it says.
Although "imagination is not usually a gift associated with bureaucracies," because previous al Qaeda attacks used vehicles to deliver explosives, "the leap to the use of other vehicles such as boats ... or planes is not far-fetched," it said.
Neither Bush nor predecessor President Bill Clinton grasped the depth of the terrorist threat posed before the suicide hijackings that killed almost 3,000 people, it said.
The 10-member bipartisan National Commission on Terrorist Attacks Upon the United States published the final report - which runs to almost 600 pages-after hearing testimony from more than 1,000 witnesses and examining as many classified documents.
Speaking to journalists, President George W Bush said he would study some "useful recommendations" made by the commission. "Where government needs to act, we will," he said.
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