Aviation officials in the US had numerous indications that airlines might be hijacked in the run-up to the 11 September attacks, it has emerged.
The FAA said it passed the intelligence to US airports
The Federal Aviation Administration received 52 intelligence reports on al-Qaeda between April and September.
The previously undisclosed report by the commission that investigated the 2001 attacks said the new threats did not lead to increased security.
But the FAA said the information could not have helped prevent the attacks.
Spokeswoman Laura Brown said: "We had no specific information about means or methods that would have enabled us to tailor any counter-measures."
Some relatives of those who died in the attacks have criticised the authorities for taking so long to release the report.
Two members of the Democratic opposition have questioned whether it was deliberately held to one side until after last November's presidential election.
They are calling for an investigation.
The report by the 11 September Commission, parts of which were published last July, said the dozens of warnings came in the five months before the attacks took place.
The document was made available by the National Archives on Thursday, after being reported by the New York Times.
Of the 105 daily intelligence summaries between 1 April and 10 September 2001, 52 mentioned Bin Laden, al-Qaeda, or both, "mostly in regard to overseas threats".
The commission report said five security warnings mentioned al-Qaeda's training for hijackings and two reports concerned suicide operations not connected to aviation.
However, none of the warnings specified what would happen on 11 September.
The report said there was a "striking" false sense of security at the FAA.
"Intelligence that indicated a real and growing threat leading up to 11 September did not stimulate significant increases in security procedures," the report said.
It said airline congestion, delays and financial problems in the industry appeared to be more pressing concerns for FAA officials than the possibility of a terrorist attack.
FAA spokeswoman Ms Brown said the agency did take action on the intelligence reports, passing them on to airlines and airports.
She said the agency was tightening security at the time of the attacks, "spending $100m a year to deploy explosive detection equipment at the airports", and preparing improved screening measures.
A member of the 11 September Commission said the release of the document had been delayed while it went through a declassification procedure.
But Carol Ashley, whose daughter died in the attacks, said the report should have been released sooner.
"I'm just appalled that this was withheld. That contributes to the idea that the government knew something and didn't act, it contributes to the conspiracy theories out there.
"We need to rebut those with the actual facts, but we need the facts to do that," she said.