BAGHDAD - U.S. attack helicopters killed four suspects and wounded three in operations south of Baghdad, the military said Sunday.

The aircraft were operating in support of Iraqi army soldiers on the ground, who were engaged by insurgents, the U.S. military said in a statement. The incident took place Friday, it said.

Suspected militants fired on the helicopters as they swooped in, then ran into a nearby structure, the statement said. One of the helicopters fired on the building, destroying it.

Afterward, Iraqi soldiers found three sniper rifles, multiple hand grenades and black masks scattered amid the ruins of the building, the military said.

Elsewhere, a car bomb killed two Kurdish security agents Sunday morning in Iraq's oil-rich northern city of Kirkuk, police said.

The men were traveling in a civilian car through downtown Kirkuk when a parked car bomb exploded next to their vehicle, said police Brig. Sarhat Qadir. Three pedestrians were injured, he said.

Kirkuk, an ethnically mixed city, lies 180 miles north of Baghdad.

South of the capital, a roadside bomb went off next to an Iraqi police patrol in Nasiriyah, wounding two policemen, authorities said. Nasiriyah is predominantly Shiite city about 200 miles southeast of Baghdad.