The blast came amid a three-month-old US and Iraqi security crackdown, meant to flush out fighters and restore order to the capital.

US military officials said that armed groups, feeling the pressure from the crackdown, have fought back by carrying out more car bombings targeting civilians with devastating death tolls.

Earlier, in the nearby Khadra neighbourhood, armed men in two cars ambushed a civilian car carrying three plainclothes police officers from the major crimes unit, killing two and wounding the third, police said.

Police and other Iraqi security officers have been targeted by fighters, who accuse them of collaborating with US-led forces in the country.