A police officer says today's explosion took place in the city's southern Dora neighbourhood, which has a small Christian population.
The officer says more than 30 people were wounded in the bombing.
A medical official confirmed the casualty figures. Both officials spoke on condition of anonymity because they are not authorised to talk to the media.
Iraq's dwindling Christian community, which is estimated to number about 400,000 to 600,000 people, has often come under attack by al-Qaeda and other insurgents.