American intelligence services had been warned that Osama Bin Laden was considering attacking US targets with aircraft three years before the 11 September attacks, a congressional investigator said.

Eleanor Hill, head of the inquiry into how US intelligence failed to stop last year's attacks, said officials never looked closely at the potential threat of hijacked airliners flying into buildings.

The totality of the information... clearly reiterated a consistent and critically important theme: Osama Bin Laden's intent to launch terrorist attacks inside the United States

Eleanor Hill

She concluded that US intelligence agencies had made "mistakes", failing to put enough resources into tracking operatives of the al-Qaeda network.

But Ms Hill admitted the information available lacked details such as specific US targets or the timing of any attack - and some of its sources lacked credibility.

In 1998, US agencies discovered that "a group of unidentified Arabs planned to fly an explosive-laden plane from a foreign country into the World Trade Center" - but did little about it, the 30-page report says.

A US airport was also mentioned as a target.

Government under fire

Later that year "intelligence agencies received further information concerning a Bin Laden plot involving aircraft in the New York and Washington DC areas," she added.

Ms Hill's staff studied 400,000 pages of documents

And just a month before the 11 September attacks, US intelligence agencies learned of a possible plot by Bin Laden to fly a plane into the US embassy in Kenya.

Ms Hill's statement came in the first public hearings held by the joint House of Representatives and Senate Intelligence Committee in its examination of 11 September.

The US Government has always said it could never have predicted the 11 September attacks.

But the BBC's Rob Watson in Washington says the report casts serious and dramatic doubts on those claims.

Weight of evidence

Ms Hill said that much of the information was vague in nature - lacking specific data on targets, operatives or dates - and often it was buried under a deluge of intelligence collected by 14 government agencies.

She also said that some of the sources providing the intelligence had been questionable.

But nonetheless "the totality of the information... clearly reiterated a consistent and critically important theme: Osama Bin Laden's intent to launch terrorist attacks inside the United States".

Ms Hill's report says that despite all of this information, the US "intelligence community did not produce any specific assessments of the likelihood that terrorists would use airplanes as weapons".

Victim's anger

The committee also heard strong criticism from Kristen Breitweiser, who represents the 11 September victims and whose own husband was killed in the World Trade Center.

"My husband and the approximately 3,000 others like him went to work that morning and never came home, " she said.

"But were any of our governmental agencies doing their job on that fateful morning? Perhaps the carnage and devastation of 11 September speaks for itself in answering this question."