Pentagon spokesman Bryan Whitman called the report demonstrably false, and that investigators at the FBI and the Southern Command have not found any evidence to support it. SouthCom is based in Miami and oversees operations at the U.S. military base in Guantanamo Bay, Cuba.

"You can't go back and undo or retract the damage that has been caused not only to this nation, but to those who have been attacked, injured or killed as a result of these false allegations," he said.

The White House, said to be outraged over the report, stopped short of outright demanding a retraction. However, a spokesman implied the magazine should take back the story.

"It's puzzling. While Newsweek now acknowledges that they got the facts wrong, they refuse to retract the story," press secretary Scott McClellan said. "I think there's a certain journalistic standard that should be met. In this instance it was not.

"This was a report based on a single anonymous source that could not substantiate the allegation that was made," McClellan added. "The report has had serious consequences. People have lost their lives. The image of the United States abroad has been damaged. I just find it puzzling."