Americans are getting their first chance Tuesday to read an ex-Navy SEAL's controversial eyewitness account of the raid that killed Osama bin Laden, with demand for the book making it an instant best-seller.

In fact, the book has already bumped the year's top-selling read so far -- the erotic novel 'Fifty Shades of Grey' -- out of Amazon.com's bestselling book list on the merits of pre-sales alone.

Demand for the book was so high, the publisher decided to bump up its American and Canadian release date a full week, to Tuesday. The book is already topping the bestseller list on Amazon.ca.

Interest has been piqued by the promise of a detailed insider's view of the May, 2011 operation that saw a team of U.S. special operatives raid the Abbottabad, Pakistan compound where Osama bin Laden was hiding out.

That curiousity has also been stoked by warnings from the Pentagon that the book's pseudonymous author Mark Owen could be in legal hot water for violating several non-disclosure agreements.

The author, whose real identity has been revealed as ex-Navy SEAL Matt Bissonnette, and his lawyer have countered that no such information is disclosed within the pages of "No Easy Day."

“We always prided ourselves on being quiet professionals, but the more I saw coverage of the raid, the more I wanted to set the record straight," he writes, explaining his compulsion to pen the novel.

"To date, how the mission to kill Bin Laden has been reported is wrong. Even reports claiming to have the inside story have been incorrect."

Last week, Pentagon press secretary George Little said Owen was in violation of confidentiality agreements he signed in 2007 as well as April of this year when he left the force.

Little suggested the book's author and publisher, Penguin Group USA, could avoid a legal battle by not putting it up for sale. He did not explain what other legal avenues the Pentagon might pursue, saying only, "The onus is on the author."

In a statement released last week, chair of the U.S. House Homeland Security Committee Rep. Peter King said anyone entrusted with classified information is obliged to keep it secret.

"Whether it is administration officials or special forces operators, national security leaks are wrong and should be prosecuted to the fullest extent possible," King said.

But in the book, Bissonette complains that the administration did not seem to have practised what it preaches.

"It took less than four hours before the news was reporting that it was SEALs who had carried out the mission," he writes.

"The mission had been secret for almost a month now, and suddenly it was all over the news," he continued, later adding:

"In Washington, anyone on Capitol Hill or in the Pentagon who had even a shred of information was leaking it."

Differing accounts

In the book's climactic recounting of Bin Laden's last moments, details stray from the initial, official White House statements that had indicated the al Qaeda mastermind was shot after reaching for a weapon.

In his version, Bisonnette wrote that the SEALs spotted bin Laden at the top of a darkened hallway and shot him in the head even though they could not tell whether he was armed.

Two guns were later found on a shelf within bin Laden's reach, but they were not loaded.

"He hadn't even prepared a defense. He had no intention of fighting," he wrote. "He asked his followers for decades to wear suicide vests or fly planes into buildings, but didn't even pick up his weapon."

Bissonette also discloses that none of the SEAL team "were huge fans of Obama," and recognizes that their successful mission had gone a long way to boosting his chances of re-election.

"When we boarded our helicopters in Jalalabad, poltics was the last thing on our minds ... Does it play a role in the aftermath? Of course it does, but I don't think it matters if a Republican or a Democrat gave the order."

As far as classified material goes, the Pentagon and CIA have both said they are poring over the text for any possible disclosures and could pursue legal action against the author and publisher if warranted.

Although the book was not formally vetted by the Pentagon prior to publication, Bissonette's lawyer has said legal advice was sought and the text was "scrupulously reviewed" prior to printing.

The book's initial print run of 200,000 was increased to 575,000 copies before the first copy hit store shelves.