The US military says it is investigating "aggressively" after a picture appeared in a British paper showing Saddam Hussein half naked.
The Sun said it "thought long and hard" before publishing
The Sun newspaper's front page image showed the former Iraqi president in a pair of white underpants.
Other pictures showed Saddam Hussein washing his trousers, shuffling around and sleeping.
The US said the photos appeared to breach Geneva Convention rules on the humane treatment of prisoners of war.
The conventions say countries must protect prisoners of war in their custody from "public curiosity".
'Destroy the myth'
The Sun cited US military sources saying they handed over the pictures showing Saddam as "an ageing and humble old man" in the hope of dealing a blow to the resistance in Iraq.
"It's important that the people of Iraq see him like that to destroy the myth," the paper's source was quoted as saying.
However, a spokesman for the multinational forces in Baghdad, Lieutenant-Colonel Steven Boylan, insisted "they were not released by the US military. So the claims in the Sun... are not correct".
A statement from the US-led force said it was "disappointed at the possibility that someone responsible for the security, welfare, and detention of Saddam would take and provide these photos for public release".
The statement added: "This lapse is being aggressively investigated to determine, if possible, who took the photos, and to ensure existing procedures and directives are complied with to prevent this from happening again."
Col Boylan said: "As far as any breaches of the Geneva Convention, that's something we are looking into. We did not officially release those photos, and so there's a question on whether it is actually a breach or not."
The Sun refused to say how it got hold of the pictures, or when they were taken, insisting it needed to protect its sources.
It defended its decision to publish them.
"We thought long and hard about publishing, and took the decision that they're such incredible pictures of the world's most brutal dictator... they were a compelling image that any newspaper or broadcaster would publish," the paper's managing editor, Graham Dudman, told the BBC News website.
Saddam Hussein is awaiting trial on numerous charges in Iraq, including murdering rivals, gassing Iraqi Kurds and using violence to suppress uprisings.
It is not clear when he will go on trial.
Saddam had a beard when he was caught near his hometown of Tikrit
The US said the pictures might be more than a year old.
They show Saddam with a moustache, rather than the beard he sported when he was captured in December 2003, and again when he appeared in court last July.
The Sun said the former Iraqi leader, 68, was allowed black hair dye to disguise his grey hair.
The paper said Saddam Hussein is kept in a 12ft by 9ft (4m x 3m) cell "somewhere near Baghdad", that he has a desk and a pink plastic chair "which he tends to use as a bedside table".
He is watched round the clock through CCTV cameras, even when he goes to the toilet, the paper said.
The source added that Saddam was one of the best behaved prisoners the US had had, it said.