On the eve of Sept. 11, Fox News has learned the U.S. Defense Intelligence Agency has attempted to block a book about the tipping point in Afghanistan and a controversial pre-9/11 data mining project called "Able Danger."

In a letter obtained by Fox News, the DIA says 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 Mohammed Atta as a threat to the U.S.before the Sept. 11, 2001, terror attacks

Click here to read the full DIA letter (pdf)

Specifically, the DIA wanted references to a meeting between Lieutenant Colonel 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 was made in the final 9/11 report.

In a highly unusual move, the DIA is now negotiating with the publisher, St. Martin's Press, to buy all 10,000 copies of the first printing of the book to keep it off shelves –– even after the U.S. Army had cleared the book for release.

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.

The documents and exclusive interviews, including an Army data collector on the Able Danger Project, are part of an ongoing investigation by the documentary unit "Fox News Reporting" which uncovered new details about American cleric Anwar al-Awlaki and efforts by the FBI to track and recruit him for intelligence purposes after 9/11.