A secret military unit repeatedly tried to arrange meetings with the FBI in the year before the September 11 attacks to warn them about the men who went on to lead the hijackers, an former intelligence officer has said.

In an interview with The New York Times and Fox News, Lieutenant Colonel Anthony Shaffer, an Army intelligence officer, said that he tried to organise three meetings with the Washington field office of the FBI to share the identities of Mohamed Atta and three other future hijackers in late 2000 and early 2001.

According to Colonel Shaffer, a small, highly secret intelligence unit known as Able Danger had used data-sorting techniques to identify Atta and his accomplices as possible US-based terrorists by mid-2000, but military lawyers prevented the team from sharing their information.

Colonel Shaffer said that lawyers working for the Special Operations Command of the Defence Department, cancelled the meetings because they believed that the surveillance techniques used by Able Danger could be understood as a violation of the rights of people who were living legally in the US.

"I was at the point of near insubordination over the fact that this was something important, that this was something that should have been pursued," Colonel Shaffer told The New York Times and Fox News.

"It was because of the chain of command saying we're not going to pass on information - if something goes wrong, we'll get blamed," said Colonel Shaffer, whose job was to liaise between Able Danger and other agencies, rather than analyse the intelligence himself.

Colonel Shaffer, 42, is the first intelligence officer to publicly identify himself in the growing controversy over how information gathered on the 9/11 hijackers was not shared by American government agencies or passed on to the 9/11 Commission which investigated the attacks.

According to Colonel Shaffer and Congressman Curt Weldon, the Republican politician who has brought to light the work of Able Danger, the full extent of the unit's findings were not passed on to the 9/11 Commission even after members of the Commission met Colonel Shaffer in Afghanistan in 2003.

Last week, the leaders of the Commission said that the panel had concluded that the intelligence programme "did not turn out to be historically significant."

But in his interview on Monday, Colonel Shaffer challenged that view, saying: "I would implore the 9/11 commission to support a follow-on investigation to ascertain what the real truth is. I do believe the 9/11 Commission should have done that job: figuring out what went wrong with Able Danger."

A former member of the Commission, Richard Ben-Veniste, the former Watergate prosecutor, yesterday called on the Pentagon hand over all the information that the Army possessed about Atta and the other hijackers.

"If these assertions are credible," said Mr Ben-Veniste, "the Pentagon would need to explain why it was that the 9/11 commissioners were not provided this information despite requests for all information regarding Able Danger."

The Defence Department has not disputed Colonel Shaffer's account of the work of Able Danger and its attempts to share its findings.

The Pentagon said in a statement that it was "working to gain more clarity on this issue" and that "it's too early to comment on findings related to the program identified as Able Danger."

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