The 173 Iraqi prisoners were found in a US raid on an Iraqi interior ministry building in the central Jadiriya district of Baghdad.
It followed repeated enquiries by the parents of a missing Iraqi teenager.
Most of those held were Sunni Arabs.
Iraq's prime minister has promised to find those responsible for any abuse and to put all his weight behind the inquiry.
The allegations are a deep embarrassment for the Iraqi government, but, however shocking, they will not come as a major surprise to many Iraqis, the BBC's Caroline Hawley in Baghdad says.
There have been persistent allegations of abuse by members of the Shia-dominated security forces, she says.
But Sunday's discovery is hard evidence and officials believe it may be the tip of the iceberg.
Wednesday, November 16, 2005
Huh. I guess Bush wasn't lying when he insisted that training of Iraqi military and police (and detention officers) was making progress. At this rate, they may outpace their mentors. From the BBC: