BAGHDAD (REUTERS) - Iraqi security forces backed by Shi'ite Muslim militias repelled an early morning assault by Islamic State in Iraq and Syria (ISIS) insurgents on a dam area north of Baghdad, security sources and a local official said on Sunday.

Fighters from the ultra-radical Islamist group attacked pro-government forces deployed around the dam on the Euphrates River near the town of al-Udhaim, about 90km north of Baghdad, in the early morning.

At least nine militia fighters and six soldiers were killed in the fighting on Sunday, which lasted about seven hours, army and police sources said.

Iraq's Shi'ite-led government, backed by US-led air strikes, has been trying to push back ISIS since it swept through mainly Sunni Muslim provinces of northern Iraq in June, meeting virtually no resistance.

"Daesh fighters attacked the dam area from the northwestern side using suicide car bombers to attack army positions... Our forces managed to push them back," Udhaim council chief Mohammed Dhefan said, using a derogatory acronym for ISIS.

Separately, three people were killed when a bomb went off in the town of al-Wihda, 25km south of Baghdad, police sources said.

The police also said they found the bodies of four people who had been shot in the head or chest in the district of Hussainiya on Baghdad's northern outskirts.