Also on Saturday, Iraqi police arrested four people in connection with the Friday suicide bombings in two mosques.
One of the four is an apparent third suicide bomber, police said.
The Saturday morning explosion occurred near the Diyala Bridge area just southeast of the Iraqi capital as dozens of people were shopping at the popular market, police Colonel Nouri Ashour said. The dead included five women, he added.
On Friday, two bombers wandered into the Shaikh Murad mosque and the Grand Mosque in the border town of Khanaqin during noon prayers and detonated explosives strapped to their bodies, police and survivors said.
Reported tolls ranged from 76, provided by Kurdish officials, to at least 100, provided by police. Hospital officials said on Friday that 74 people were killed and more than 100 wounded in the largely Kurdish town, about 140km (90 miles) northeast of Baghdad.
A security officer in Khanaqin, who asked not to be identified because of the nature of his job, said four people were arrested after the blasts - three who came from outside the town and the other a would-be bomber who was found near the scene.
An Iraqi soldier walks through the
rubble at Khanaqin's Grand Mosque
Khanaqin police had received information from the authorities in nearby Baqouba about a possible suicide bomber in the town, but it came minutes before the attacks, he added.
The blast ripped down part of the roof of the Grand Mosque and heavily damaged the other place of worship. At sunset, dozens of people were still searching the rubble for missing family members and friends.
One of the survivors, Omar Saleh, said he was on his knees bowing in prayer when the bomb exploded at the Grand Mosque.
"The roof fell on us and the place was filled with dead bodies," Saleh, 73, said from his hospital bed.
American soldiers from the 101st Airborne Division sent medical specialists and supplies to the town, about 10km (six miles) from the Iranian border.
The attack came hours after two car bombs exploded outside the Hamra hotel on Friday in the second attack against a compound housing foreign journalists in the Iraqi capital in less than a month.
Eight Iraqis were killed and at least 43 people were injured, officials said.
The latest attacks in Khanaqin and Baghdad have brought to at least 1617 the number of Iraqis killed since the Shia-led government took power on 28 April, according to an Associated Press count.