The mistreatment of Iraqi prisoners in US custody is not limited to isolated cases but forms part of a systematic pattern, the Red Cross has said.
Photos of the treatment of Iraqis have shocked the world (AP Photo/ Courtesy of The New Yorker)
A spokesman said the International Committee of the Red Cross (ICRC) had been warning the US about such cases for more than a year.
He was responding to the publication of parts of a leaked ICRC report.
The document concluded that abuse of Iraqi detainees was widespread and in some cases tantamount to torture.
The Red Cross mentions a number of "serious violations of humanitarian law", including beatings and prolonged solitary confinement.
The report says abuses have been committed at a number of facilities - not just Abu Ghraib prison near Baghdad, which is the focus of allegations against US soldiers.
Other facilities where mistreatment allegedly occurred include al-Baghdadi air base, Hubbania camp, Tikrit holding area, the ministry of defence and the presidential palace in Baghdad.
The ICRC has a strict policy of never publicly releasing its reports into prison conditions.
But on Friday the Wall Street Journal quoted parts of the 24-page report. It alleges, among other things, that prisoners were kept naked in cells, in darkness and without facilities.
It says prisoners were beaten, in one case leading to death, and that soldiers fired on unarmed prisoners from watchtowers, killing some of them.
The report concludes there have been serious violations of the Geneva Conventions governing the treatment of prisoners of war.
The report says the ill-treatment was widely tolerated, especially with regard to extracting information from Iraqis.
The report is at odds with the position of the US government, which insists that cases of abuses were isolated.
ICRC director of operations, Pierre Kraehenbuehl, disputed this.
"We were dealing here with a broad pattern, not individual acts. There was a pattern and a system," he said.
Mr Kraehenbuehl said that over the last year the Red Cross had repeatedly warned the Bush administration that the conditions at the Abu Ghraib needed changing.
"Our findings were discussed at different moments between
March and November 2003, either in direct face-to-face
conversations or in written interventions," he said.
He added that ICRC delegates in Iraq had also expressed concern about the conditions of prisoners held in UK-run detention centres.
The British newspaper the Daily Mirror has published photographs apparently showing British troops abusing prisoners.