The Red Cross said it had repeatedly alerted U.S.-led occupation authorities to practices it described as "serious violations of international humanitarian law" and "in some cases tantamount to torture."

It confirmed the confidential February 4 report, which appeared on the Wall Street Journal Web Site Monday, was genuine.

The 24-page report concluded that "persons deprived of their liberty face the risk of being subjected to a process of physical and psychological coercion, in some cases tantamount to torture, in the early stages of the internment process."

During a visit to Abu Ghraib in October, Red Cross delegates witnessed "the practice of keeping persons deprived of their liberty completely naked in totally empty concrete cells and in total darkness," the report said.

"Upon witnessing such cases, the ICRC interrupted its visits and requested an explanation from the authorities. The military intelligence officer in charge of the interrogation explained that this practice was 'part of the process'."

It said it met prisoners who were being held naked in complete darkness. Others had been held naked and were allowed to dress, but given only women's underwear.

The Red Cross's visit took place two months before pictures were taken of U.S. troops abusing prisoners, which later led to criminal charges against seven soldiers.

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Those pictures appeared in the media last month, causing international outrage and prompting apologies by President Bush and other senior officials. However, Washington has said it believed the practices were isolated incidents of aberrant behavior by individuals and not its usual practice.

Although much of the abuse described in the report appears to have taken place in jails run by U.S. forces, the report also describes the death of an Iraqi prisoner in custody in the British zone Basra last September. His name is blacked out.

A spokesman for Britain's defense ministry said the allegation was not new, but appeared to be a reference to the death of an Iraqi detainee named Baha Musa, which Britain says it has been investigating since last year.

The Red Cross report described him as one of nine men arrested in a Basra hotel and "made to kneel, face and hands against the ground, as if in a prayer position. The soldiers stamped on the back of the neck of those raising their head."

It said the death certificate for the Iraqi prisoner listed his cause of death as a heart attack.

"An eyewitness description of the body given to the ICRC mentioned a broken nose, several broken ribs and skin lesions on the face consistent with beatings."

The report describes prison guards opening fire with live ammunition during riots and escape attempts, on detainees who "were unarmed and did not appear to pose any serious threat to anyone's life."

According to the report, the Red Cross repeatedly drew allegations of mistreatment to the attention of the authorities. In some cases, they changed practices. For example, they stopped issuing wristbands marked "terrorist" to all foreign detainees.

Among the "serious violations of international humanitarian law," the report listed a failure to set up a system to notify family members of arrests.