By Phil Stewart

(Reuters) - The Pentagon warned on Thursday that it was considering legal action against a former U.S. Navy SEAL for material breach of non-disclosure agreements with his first-hand account of the raid that killed Osama bin Laden.

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....REST OF IT