Former US defence secretary Donald Rumsfeld said his biggest mistake during his six years in the Pentagon was not resigning after shocking photos of the treatment of Iraqi inmates by American soldiers at Baghdad's Abu Ghraib prison were published.
The New York Times and The Washington Post published articles about Mr Rumsfeld's forthcoming autobiography, Known And Unknown, based on copies they obtained before its release next Tuesday.
In the book, Mr Rumsfeld said he submitted his resignation to President George Bush twice in 2004, five days apart, after the misconduct of soldiers at Abu Ghraib became public. Mr Bush rejected both but finally removed Mr Rumsfeld from the Cabinet after elections in 2006 cost Republicans control of Congress.
The Washington Post quotes Mr Rumsfeld as saying in the book: "More than anything else I have failed to do, and even amid my pride in the many important things we did accomplish, I regret that I did not leave at that point."
Mr Rumsfeld, 78, also criticised the Bush administration for failing to work with the US Congress on drafting policies for treatment of prisoners.
"Looking back, I see there are things the administration could have done differently and better with respect to wartime detention," he said.
The accounts of the book also quote Mr Rumsfeld as criticising his administration colleagues, including both of Mr Bush's secretaries of state, General Colin Powell and later Condoleezza Rice.
Gen Powell often complained with unattributable comments about the Pentagon, Mr Rumsfeld wrote, and he said Ms Rice was too involved with putting democracy and human rights before US security in dealing with some countries.
The book is generally favourable towards Mr Bush himself, but Mr Rumsfeld wrote that the president should have done more to resolve disputes between senior advisers.
He also said Mr Bush sometimes may not have forced aides to provide fully laid-out options before making decisions.