There was no immediate claim of responsibility. Car bombings targeting Shiites are frequently the work of al-Qaida's branch in Iraq, known as the Islamic State of Iraq and the Levant.
Wednesday's blast struck a day after bombings and a shooting killed at least 24 civilians in Iraq.
Militants are keeping up a high pace of attacks in an effort to capitalize on tensions between Iraq's Sunni and Shiite Muslims, inflamed in part by the sectarian tensions reflected in the civil war in neighboring Syria.
Members of Iraq's Sunni Arab minority have been protesting against the Shiite-led government, angered over what they see as second-class treatment against their sect and the unfair application of tough anti-terrorism measures.
Attacks surged after a deadly crackdown on a Sunni protest camp by security forces in April. The United Nations says more than 4,000 people have been killed over the past five months, including 804 in August.
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Associated Press writer Sinan Salaheddin contributed reporting.
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