Sept. 4, 2012 -- Top Pentagon officials said today that a controversial firsthand account of the nighttime raid that killed Osama bin Laden written by a former U.S. Navy SEAL reveals classified information and could endanger other special operations servicemen.
The book, "No Easy Day," was written by an ex-SEAL Team Six member under the pseudonym Mark Owen and is the first to detail the last violent moments of the al Qaeda leader's life. It went on sale today.
While the Pentagon's assessment of Owen's book continues, Department of Defense Press Secretary George Little told reporters the department "believe[s] that sensitive and classified information is contained in the book" and called its publication without review the "height of irresponsibility."
Little declined to provide specifics about what classified information is revealed, but said the book raised "serious concerns" and represented a "material breach of nondisclosure agreements that were signed by the author of this book."
"This is a solemn obligation," said Little. "And the author in this case elected not to abide by his legal obligations. And that's disheartening and, frankly, is something that we're taking a very close look at."
The Pentagon sent Owen a letter Thursday saying the government was considering legal action against him, and Little said today those options are still being reviewed.
Owen's attorney said in his own letter to the Pentagon Friday that agreements signed by Owen in 2007 did not require him to present any materials for pre-publication review and said the book did not reveal any sensitive information. The book's publisher, Dutton, has also said that it had been vetted by a former special operations attorney before publication, even if it was not vetted by officials at the Department of Defense, the White House or the CIA.
SEAL Boss: 'I Am Disappointed, Embarrassed and Concerned'
Meanwhile, in an internal message to his command entitled "The Cost of Disclosure," Rear Admiral Sean Pybus, who heads Naval Special Warfare Command (NSW), criticized SEALs whom he said had violated the command's ethos.
"We do NOT advertise the nature of our work, NOR do we seek recognition for our actions," Pybus wrote to his command in the letter, a copy of which was obtained by ABC News.
"I am disappointed, embarrassed and concerned", writes Prybus. "Today, we find former SEALs headlining positions in a Presidential campaign; hawking details about a mission against Enemy Number 1; and generally selling other aspects of NSW training and operations."
Aside from hurting NSW's reputation and security, Pybus said "the security of our Force and Families is also put at risk by the release of sensitive information" and said enemies can gather information and NSW details that "expose us to unnecessary danger."
SEAL's Account Differs From 'Official' Version
"No Easy Day," written with journalist co-author Kevin Maurer, takes readers inside bin Laden's compound in Abbottabad, Pakistan on the night of the May 2011 raid. At times, Owen's account differs from the "official" version given by the White House, especially when it comes to the moment of bin Laden's death.
White House spokesperson Jay Carney told reporters days after the operation that though bin Laden was unarmed, he had "resisted" before he was shot. By Owen's account, another SEAL shot the terror leader as his head was poking out a doorway, apparently before he could have made any moves to resist.
Little said blocking the book's release today was not really an option available to the Pentagon given how copies had already gotten out into the public domain. He also said no effort will be made to block its sale at military installations .
"It is not our typical practice to get into the business of deciding what and what does not go on bookshelves in military exchanges. But that doesn't mean in any way, shape or form that we don't have serious concerns about the fact that this process of pre-publication review was not followed," he said.
Maurer said that after spending months with Owen writing the book, he was convinced Owen did not write the book out of vanity, but to "share a story about the incredible men and women defending America all over the world."
Dutton, the book's publisher, said in the book's announcement that a majority of the proceeds will go to the families of fallen SEALs.
ABC News' Lee Ferran contributed to this report.