A suicide bomber apparently caused the blast at the Shiite mosque in the Taj area north of the capital, which also injured 30 worshippers, the source, who declined to be identified, told Xinhua.
The bombing took place amid a wave of violence across northern and central Iraq. Nine people died Saturday in the series of shootings and bomb blasts.
The worst incident Saturday took place in a village south of Mosul. A suicide bomber drove into a police patrol, killing one officer and wounding three other people.
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