The publisher of an insider account of the US Navy SEAL raid that killed terror mastermind Osama bin Laden said it would begin public sales next week despite a Pentagon warning of possible legal action against the author and others.

Before the Pentagon's warning, Penguin Group (USA) brought forward publication to September 4 from September 11, saying it was "important to put No Easy Day on sale and let the book speak for itself".

"At this time, we see no reason to change our plans," Christine Ball, a spokeswoman for Penguin Group's Dutton imprint, said yesterday.

In his book, Mr Bissonnette, writing under the pseudonym Mark Owen, says that during the raid on bin Laden's compound in Abbottabad, Pakistan, last May, the SEALs spotted the terror chief at the top of a darkened hallway and shot him in the head, even though they could not tell whether he was armed.

US government officials have described the SEALs shooting bin Laden only after he ducked back into a bedroom, because they assumed he might be reaching for a weapon.

Pre-orders for the book have catapulted it to No 1 on Amazon's bestseller list, displacing erotic trilogy Fifty Shades Of Grey. An initial print run of 200,000 has been increased to 575,000 copies.

It was highly unlikely that the US government would try to halt publication of the book itself, considering that a limited number of advance copies are already in the public domain and media reports have summarised the book's contents.

Pentagon press secretary George Little said the book's author, ex-SEAL Matt Bissonnette, had broken two non-disclosure agreements that he signed in 2007 by failing to submit the book for an official security review before it was published.

Mr Bissonnette's lawyer disputed that yesterday, saying he believed the decorated former commando had "earned the right to tell his story".

Mr Little would not say what legal options the Pentagon was considering, or when it might take action.

He suggested that the Pentagon might be satisfied if Mr Bissonnette were to stop the book's official release. The Pentagon obtained an advance copy last week and has since been reviewing it for any classified information and to determine what, if any, legal action should be taken, Mr Little said.

"The onus is on the author," he said, while declining to spell out what the author must do.

Jeh Johnson, the Pentagon's top lawyer, notified Mr Bissonnette on Thursday that the Pentagon believed he was in "material breach and violation" of two non-disclosure agreements and of a related document he signed upon leaving active duty in April this year.

In a letter faxed to Mr Bissonnette through his publisher, he was advised by Mr Johnson that "further public dissemination of your book will aggravate your breach and violation of your agreements".

Mr Johnson said the Pentagon was "considering pursuing against you, and all those acting in concert with you, all remedies legally available to us in light of this situation".

In response, Robert Luskin of law firm Patton Boggs wrote to Mr Johnson yesterday, saying that his firm was representing Mr Bissonnette and asserted that he was not in breach of his non-disclosure agreements.

Mr Luskin, who represented White House aide Karl Rove in the leak of CIA agent Valerie Plame's identity in the Bush administration, said the author had "sought legal advice about his responsibilities before agreeing to publish his book and scrupulously reviewed the work to ensure that it did not disclose any material that would breach his agreements or put his former comrades at risk. He remains confident that he has faithfully fulfilled his duty".

If the Pentagon determines the bin Laden book does disclose secrets, the government could consider bringing criminal charges against Mr Bissonnette.

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