In a letter obtained by Reuters, and subsequently released by the Pentagon, the Pentagon's top attorney said the Department of Defense was also considering legal action against anyone "acting in concert" with the author. It hinted that the book's royalties might be subject to government claims.

The letter, addressed to "Mark Owen," the pseudonym under which the book was written, identified two separate non-disclosure agreements he signed with the Navy that legally committed him to never divulge classified information, which is a crime.

"You are in material breach and violation of the non-disclosure agreements you signed," said the letter by Jeh Johnson, the Pentagon's General Counsel.

"The Department of Defense is considering pursuing against you, and all those acting in concert with you, all remedies legally available to us in light of this situation."

The author may have hoped to publish the book anonymously but his identity as Matt Bissonnette was quickly revealed and confirmed independently by Reuters. It was unclear how many others the Pentagon may consider legally culpable, given the broad language in Johnson's letter.

A spokeswoman at publisher Dutton, which is an imprint of Penguin Group (USA), did not immediately respond to a request for comment.

NOT VETTED

U.S. officials have said they were surprised by his book, "No Easy Day," which was not vetted by government agencies before its publication to ensure that no secrets were revealed.

The letter noted that, under the terms of the non-disclosure agreements, the author had agreed to submit any manuscript for pre-publication security review and to obtain permission before publishing it.

The Pentagon pointed out that the disclosure of classified information was a crime and suggested that, under the terms of the non-disclosure agreement he signed, the U.S. government could be entitled to all "royalties, remunerations, and emoluments" from such a disclosure.

The letter did not say what classified information the book revealed but the book says an unarmed bin Laden was looking out from his bedroom door when he was shot in the head during the May 2011 raid on his hide-out in Pakistan.

The book has received widespread media coverage and the Pentagon letter noted that some copies have already been released, ahead of the book's formal release next week.

"Further public dissemination of your book will aggravate your breach and violation of your agreements," the letter warned.

Earlier this week, the author said in a statement from his publisher that the book was written "with respect for my fellow service members while adhering to my strict desire not to disclose confidential or sensitive information that would compromise national security in any way."

But many in the special operations community have privately expressed disappointment in recent days over the book and the publicity it has received.

The author now faces threats against his life. An official al Qaeda website last week posted a photograph and the real name of the former Navy commando, calling him "the dog who murdered the martyr Sheikh Osama bin Laden.

(Editing by Sandra Maler and Mohammad Zargham)

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