A first-hand account of the May 2011 raid by US forces that killed Osama Bin Laden contradicts the official story, the Associated Press claims.
It has purchased an advance copy of an unauthorised account of the raid, No Easy Day, by a former Seal.
The book says Bin Laden was shot dead as soon as he looked out of his bedroom as Seals rushed up the stairs, AP says.
But US officials have stated he was shot only once he had ducked back into the bedroom.
They have said his actions suggested he might be reaching for a weapon.
The alleged contradiction will add to existing controversy over the book.
It was written under a pseudonym, Mark Owen, but only hours after the book's existence came to light the author's real name was revealed by Fox News.
Military officials also say the publishers failed to submit the book to the Pentagon to ensure it discloses no secret information - part of normal protocol - and are scrutinising its contents.
'Peeking out of the door'
The book is now due to be released on 4 September instead of 11 September, after a surge of advance orders sent the book to the top of the amazon.com and Barnes&Noble.com bestseller lists.
According to AP, the author says he was directly behind a "point man" going up the stairs.
"Less than five steps" from the top of the stairs, he heard "suppressed" gunfire: "BOP. BOP."
The point man had seen a "man peeking out of the door" on the right side of the hallway.
The author writes that Bin Laden ducked back into his bedroom and the Seals followed, only to find him crumpled on the floor in a pool of blood with a hole visible on the right side of his head and two women wailing over his body, AP relates.
The women were pulled out of the way and Seals fired several shots into Bin Laden's still-twitching body until he was motionless. The Seals later found two unused weapons by the doorway.
According to Obama administration officials, Bin Laden was shot only after he ducked back into the bedroom - prompting fears he might be grabbing a weapon.
White House spokesman Tommy Vietor would not comment on the apparent contradiction late on Tuesday.
The author says early official accounts of the operation, including reports of a protracted firefight, were misleading, the BBC's Paul Adams in Washington reports.
According to the author, the raid was being reported like a bad action movie.
It is not a surprising revelation - in the days after the raid, the White House seemed to contradict itself more than once, our correspondent says.
The book also reveals that the commandos were not big fans of President Obama, even though they applauded his decision to launch the operation.
According to AP, the book also asserts that one Seal sat on Bin Laden's chest in a cramped helicopter as his body was flown out to sea. This again apparently contradicts official US claims that his body was treated with dignity ahead of his burial.
The book is due to be published in the US by Penguin Group's Dutton imprint, which says it is a "blow-by-blow narrative of the assault".
It has previously stated the book was vetted by a former special operations lawyer for "tactical, technical and procedural information as well as information that could be considered classified by compilation and found it to be without risk to national security".
But neither the Pentagon, CIA nor White House reviewed the book ahead of its publication - and officials warn criminal charges could result from the improper disclosure of secret information.