Twelve bodies found Saturday had been dumped in one grave about 500 yards away from the local office of radical Shiite cleric Muqtada al-Sadr's movement, while two others were buried together in a nearby area on the western outskirts of Mahmoudiya, a city spokesman said.
The spokesman, Ather Kamil, said the bodies were found after members of al-Sadr's Mahdi Army militia were detained and confessed to killing and burying dozens of Sunnis as well as some Shiites killed for criminal purposes.
The grisly discoveries came two days after the Iraqi troops found the remains of 30 people believed to have been killed more than a year ago in three abandoned houses elsewhere in the area.
An Iraqi army officer, who spoke on condition of anonymity because he wasn't authorized to release the information, also said the bodies were found after the recent arrests of several Shiite militiamen who provided information about where to find the bodies.
Iraqi soldiers continued to comb the palm tree-lined desert area as the search for more bodies continued on Saturday.
Several black-clad women whose loved ones disappeared amid the fierce sectarian bloodletting that reached a peak last year rushed to the field after hearing that more bodies had been found on Saturday.
Associated Press photos showed U.S. soldiers providing cover as the Iraqi troops took the bodies away in plastic bags.
Mahmoudiya is a predominantly Shiite city of some 600,000 people about 20 miles south of Baghdad. Sunnis comprise about 20 percent of its population, but many families have fled the area amid a wave of violence by the Shiite militiamen.
The Shiite fighters were angry over fierce attacks by Sunni insurgents leading to a fierce cycle of retaliatory sectarian violence that only ebbed last year with a cease-fire by al-Sadr, a Sunni revolt against al-Qaida in Iraq and an influx of American troops.
The lull in violence and the clearing of former insurgent strongholds has led to the increasing discovery of mass graves. But most of the others have turned up in areas to the north and west of the capital that had been dominated by al-Qaida in Iraq.
The U.S. military said Thursday's mass grave was the first unearthed in the area south of Baghdad. It had no immediate comment on Saturday's discovery.