Image caption A surge in orders for the book has sent it to the top of the bestseller lists

The Pentagon says it may sue a former US special forces member who has written a first-hand account of the May 2011 raid that killed Osama Bin Laden.

The Department of Defense's top lawyer has informed the former Navy Seal that he has violated agreements he signed in 2007 not to divulge military secrets.

The book, No Easy Day, was written under the pseudonym Mark Owen.

Its publisher, Dutton Penguin, said it saw "no reason" to change its plans to release the book on Tuesday.

It was not reviewed ahead of publication by the Pentagon, CIA or the White House - and officials had warned that criminal charges could result from the improper disclosure of secret information.

In an interview with CBS, "Mr Owen" - who has been identified by US media as Matt Bissonnette - rejected charges that the book is timed to influence the November election in the US, saying it "has nothing to do with politics".

'Material breach'

The Pentagon's general counsel, Jeh Johnson, wrote to the author on Thursday to inform him that non-disclosure form he signed in 2007 obliged him to "never divulge" classified information.

The letter said: "In the judgment of the Department of Defense, you are in material breach and violation of the non-disclosure agreements you signed."

The Pentagon is considering "all remedies legally available to us", the letter added.

It was reported this week that No Easy Day contradicts the official story of the raid.

The book says Bin Laden was shot dead as soon as he looked out of his bedroom as Seals rushed up the stairs, according to the Associated Press news agency, which has seen an advance copy.

But US officials have stated he was shot only after he had ducked back into the bedroom, prompting fears he might be grabbing a weapon.

The book also reveals that the commandos were not big fans of US President Barack Obama, even though they applauded his decision to launch the operation.

An interview with Mr Bissonnette by CBS News' 60 Minutes was originally scheduled for broadcast ahead of the book's original release date of 11 September.

The author said he chose that date to signify that the publication was a non-political decision.

"You know, if these - crazies on either side of the aisle want to make it political, shame on them," he says an excerpt of the interview released by CBS.

"This is a book about September 11th, and it needs to rest on September 11th. Not be brought into the political arena, because this has nothing to do with politics."

However, publication has now been brought forward to 4 September.