Breaking its usual vow of silence, the Geneva-based humanitarian organisation on Friday said visits to detention centres in Iraq - carried out between March and November 2003 - showed infringements of international treaties on the treatment of prisoners of war.
In some cases, the ill-treatment was "tantamount to torture," particularly when interrogators were seeking information or confessions, the ICRC said in a report, parts of which were published in US financial daily the Wall Street Journal.
Pierre Kraehenbuehl, director of ICRC operations, confirmed the contents of the report at a news conference.
"Our findings do not allow us to conclude that what we were dealing with at Abu Ghuraib were isolated acts of individual members of coalition forces. What we have described is a pattern and a broad system," he said.
Pictures of grinning US soldiers abusing naked Iraqis at Abu Ghraib - the largest prison in the country and notorious for torture under Iraqi President Saddam Hussein - have sparked an international outcry.
The excerpts published by the Wall Street Journal spoke of the use of ill-treatment that "went beyond exceptional cases and might be considered a practice tolerated" by occupation forces.
That differs sharply from the view of senior officials in the Bush administration that military higher-ups had not condoned abuse, the newspaper said.
In the report, the ICRC said prisoners at Abu Ghraib were held naked in empty cells and beaten by soldiers. Three former military policemen at the prison told Reuters on Thursday abuse was commonplace.
The humanitarian group also said US-led occupation forces fired on unarmed prisoners from watchtowers and killed some of them, as well as committing "serious violations" of the Geneva Conventions governing treatment of war prisoners.
The Red Cross said on Thursday it had repeatedly urged the US to take "corrective action" at the jail.