Police found nine severed heads in fruit boxes near a volatile city northeast of Baghdad on Tuesday, authorities said, the second such discovery in less than a week.

A roadside bomb also exploded near an American military convoy in central Baghdad, killing a woman and wounding three pedestrians, Lt. Thair Mahmoud said. The three-vehicle convoy was traveling near one of Baghdad's bus stations when the bomb detonated. The convoy kept moving.

The boxes containing the heads ¡ª all from men ¡ª were discovered by a highway in the village of Hadid near Baqouba, a mixed Shiite-Sunni Arab city 35 miles northeast of Baghdad that has seen a recent rise in sectarian violence.

The heads were transferred to the city morgue and an investigation was under way, according to the Joint Cooperation Center, which is run by Iraqi and U.S. forces.

Iraqi police also found eight severed heads in the village on Saturday, with a note indicating at least one of those men had been killed in retaliation for the slaying of four Shiite doctors and a former governor during the administration of former Prime Minister Ayad Allawi.