The Pentagon has warned to take legal action against a former Navy SEAL who has written a first-person account of the May 2011 raid that killed Osama bin Laden in Pakistan, saying that he has violated his signed agreement not to divulge classified information.

The book No Easy Day is due to be released September 4.

The excerpts of the book released in the western press have already created controversy in the US on the operation that killed bin Laden.

"In the judgment of the Department of Defence, you are in material breach and violation of the non-disclosure agreements you signed. Further public dissemination of your book will aggravate your breach and violations of your agreement," Pentagon's top lawyer Jeh Charles Johnson wrote in a letter to the Navy SEAL, who has written the book in the pseudo name of Mark Owen.

Author's real name is Matt Bissonnette.

In his letter dated August 30,

The Department of Defence, he wrote, has obtained and reviewed an advance copy of the book entitled No Easy Day authored by you.

The top Pentagon lawyer told the Navy SEAL he signed two separate non-disclosure agreements on January 24, 2007, by the virtue of which he has a continuing obligation to "never divulge" classified information.

"This commitment remains in force even after you left the active duty," Johnson said.

The letter, however, did not divulge details of what was the content of the book that is being considered classified.