Baghdad, Iraq ? U.S. forces were back patrolling the streets of the predominantly Shiite city of Balad on Tuesday after five days of sectarian slaughter killed 95 people, violence that surged out of control despite the efforts of Iraq’s best-trained soldiers.

Iraq’s 4th Army took command of the region north of Baghdad a month ago, but had been unable to stem recent attacks in Balad, where the slayings of 17 Shiite Muslim workers on Friday set off revenge killings by Shiites.

Minority Sunnis, who absorbed most of the brutality in the city of 80,000 people, have been fleeing across the Tigris River in small boats, Balad police commander Brig. Nebil al-Beldawi said.

The police commander said gunmen wearing black uniforms, trademark clothing of Shiite militiamen, had clashed with residents of Duluiyah, a predominantly Sunni city on the east bank of the Tigris, opposite Balad. Al-Beldawi said the militants were keeping food and fuel trucks from entering Duluiyah. Two fuel trucks were attacked and burned.

The conflict between Shiites and Sunnis in the Balad area illustrates the threat to the region should Iraq move toward dividing into three federal states – controlled by Shiites in the south, Sunnis in the center and Kurds in the north.

Regions such as Baghdad and areas immediately to the north, including Balad, are now home to Shiites and Sunnis. Both groups would be expected to fight hard to maintain control of their territory, especially in the capital.

Last week, over the objection of nearly all Sunnis and some Shiites, the Shiite-dominated parliament voted to allow moves toward establishing federal states after an 18-month waiting period. Dividing the country would close Sunnis off from oil wealth, which would end up with the Kurds in the north and the Shiites in the south. Sunni lands are largely desert or agricultural belts along the Tigris and Euphrates rivers.