It happened in the mainly Shi’ite al-Jadida district in the east of the Iraqi capital.
The blast mangled several market stalls and scattered wreckage across the area.
In Samarra, 125 kilometres north of Baghdad, two soldiers and two civiilans have been killed in separate attacks.
The US military says two marines were killed on Wednesday when their armoured vehicle drove over a mine in northwest Iraq.
Yesterday at least 71 people were killed in a series of attacks by suicide car bombers in central Iraq.
The attacks come amid reports that insurgents holding an Australian hostage have extended a deadline for Canberra to withdraw its troops from Iraq.