The fighting took place Monday in Adwaniyah, a town near the Tigris River about 20 kilometers (13 miles) south of Baghdad, the military said in a statement.
It began when between 30 and 45 militants on foot attacked checkpoints set up by local citizens who recently began working with U.S. troops in the area, the military said. Other al-Qaida fighters followed in trucks mounted with high caliber machine guns, it said.
The local citizens were aided by another neighborhood group from Hawr Rajab, a town close to Adwaniyah, the statement said. With their help, as well as with backup from U.S. and Iraqi troops, they were able to keep the militants from taking over the checkpoints, it said.
During the battle, American F-16 fighter jets dropped two 500-pound bombs in the area, the military said. It was unclear whether the 15 victims died in the gunbattle, or as a result of the U.S. bombing.
On Sunday, Maj. Gen. Rick Lynch, commander of the Army's 3rd Infantry Division, said the military had recruited 26,000 "concerned local citizens" to man checkpoints and guard critical infrastructure in their hometowns south of Baghdad.