London, Sep 11 (IANS): The US Defense Intelligence Agency (DIA) tried to block a book giving details of a project which identified the 9/11 plotter well before the hijack of the plane used in the attack, a media report said.

According to Fox News, it has obtained a letter in which the DIA says that national security could be breached if "Operation Dark Heart" is published in its current form.

The agency also attempted to block key portions of the book that claim "Able Danger" successfully identified hijacker Mohammed Atta as a threat to the US before the Sep 11, 2001, terror attacks.

Atta was the alleged ring leader of the Sep 11 hijackers and piloted American Airlines Flight 11 into the World Trade Center.

The US defense department is now negotiating with the publisher, St. Martin's Press, to buy all 10,000 copies of the book to keep it off shelves -- even after the US Army had cleared the book for release, the report said.

Specifically, the DIA wanted references to a meeting between Lt. Col. Tony Shaffer, the book's author, and the executive director of the 9/11 Commission, Philip Zelikow, removed.

In that meeting, which took place in Afghanistan, Shaffer alleges the commission was told about "Able Danger" and the identification of Atta before the attacks. No mention of this was made in the final 9/11 report.

Shaffer, who was an undercover agent at the time, said there was "stunned silence" at the meeting after he told the executive director of the commission and others that Atta was identified as early as 2000 by "Able Danger".

"Philip Zelikow approached me in the corner of the room. 'What you said today is very important. I need you to get in touch with me as soon as you return from your deployment here in Afghanistan'," Shaffer said.

However, an inspector general (IG) report by the defense department concluded there was no evidence to support the claims of Shaffer and others.

But Fox News has obtained an unredacted copy of the IG report containing the names of witnesses, who backed up Shaffer's story when contacted for comment.

Shaffer spoke to Fox News before he was asked by the military not to discuss the book. He confirmed efforts to block the book and other details.

Calling the move "highly unusual", he explained that the book had already been cleared for release when the DIA stepped in.

"Apparently, Defense Intelligence Agency took exception to the way the army cleared the book," he told Fox News.