Some 500 Iraqis protested outside Abu Ghraib, the US-run jail, the centre of a damaging scandal over prisoner abuse.
"I would like to personally apologise to the people of Iraq for a small number of leaders and soldiers," Major General Geoffrey Miller told reporters touring the facility near Baghdad. "I personally guarantee that this will not happen again," he said.
Outside the jail, some 500 protestors carried banners including ones that said 'Abu Ghraib, witness of American savagery' and 'US Army, go home. Your families are waiting for you - this country is for Iraqis'. US President George W. Bush, addressing the charges of widespread abuse of prisoners, told the Arabic satellite television Al-Hurra on Wednesday that he found the practice "abhorrent."
"People in Iraq need to understand that I view these practices as abhorrent," he said in footage transmitted from the White House Map Room as part of a public relations offensive.
Fighting flared again overnight between Sadr's militiamen and coalition troops who raided the militia's offices in two mainly Shia towns south of Baghdad.
At least 23 Iraqis and a coalition soldier were killed in the clashes, according to hospital sources and officials.
Coalition forces seized Sadr's main office in the southern city of Diwaniya, 180 km (100 miles) from Baghdad, and confiscated a cache of arms, according to an AFP correspondent.
Nine militiamen were killed in clashes there and several others injured, according to a spokesman for the cleric. Five civilians were also killed in the fighting around the office, hospital sources said.
Violence also ripped the shrine city of Karbala, where Polish troops took over several buildings occupied by the Mehdi Army. Ten militiamen were killed along with one coalition soldier, the coalition said.
Polish forces, which command a multinational force in Karbala, started distributing leaflets late on Tuesday warning that they would conduct nightly patrols to disarm Sadr's followers.
Fresh clashes broke out in the holy city of Najaf, where Sadr has dug in with thousands of armed followers, but there were no reports of casualties.
"We want you to be more vigilant and more disciplined and, God willing, I'm leading you to martyrdom," Sadr told thousands of followers in a mosque near Najaf, according to video film footage distributed by his office.
US Defence Secretary Donald Rumsfeld announced plans to maintain a force of about 138,000 troops in Iraq through next year, and ordered the deployment of 10,000 combat troops to replace units serving extended tours of duty.