BAGHDAD, Iraq — U.S. and Iraqi troops repelled a series of coordinated attacks including suicide car bombs, killing six insurgents and capturing 12, in southern Baghdad, the military said yesterday.

In political developments, Sunni Arabs on the committee drafting a new constitution rejected Kurdish demands for federalism as long as foreign forces remain in Iraq. The statement came on the eve of a meeting to try to overcome differences on the charter.

Iraq's most feared terror group, meanwhile, warned Sunni Arabs that voting in a referendum on the charter this fall would be tantamount to rejecting Islam.

The fighting erupted about 8 p.m. Friday when guerrillas opened fire on an Iraqi army position, the military said. U.S. attack helicopters responded with rockets and gunfire.

At nearly the same time, a suicide attacker drove a truck loaded with explosives into a nearby Iraqi army checkpoint, killing an Iraqi soldier. A second suicide driver tried to attack another Iraq position in the area, but a U.S. tank opened fire and the car detonated prematurely.

Minutes later, insurgents at a fourth location fired two rocket-propelled grenades and a mortar round at another Iraqi army post in southern Baghdad. None of the rounds caused any damage, the U.S. statement said.

Over the next two hours, insurgents tried to launch further attacks on the two Iraqi army posts but were driven off by U.S. and Iraqi fire, the statement added.

U.S. troops suffered no casualties, according to the military.

The Bush administration is hoping that progress on the political front will help curb the insurgency by luring Sunni Arabs away from rebel ranks. Key to maintaining the momentum is a new constitution, which must be approved by parliament by Aug. 15 and by voters two months later.

Yesterday, Sunni Arab members of the drafting committee rejected Kurdish demands to transform Iraq into a federal state, saying such a step should not be taken during foreign-military occupation and an unstable security situation.

The Sunni delegates think federalism should be discussed when there is a parliament that represents all Iraqis, member Kamal Hamdan said.