Four people were killed and five others wounded in separate incidents north of Baghdad, a source from U.S.-Iraqi liaison office said on Monday.

"A roadside bomb detonated early in the morning near an Iraqi army patrol in the town of al-Dowr, capital of Salahudin province, some 155 km north of Baghdad, killing one soldier and wounding three others," the source from the Joint Coordination Center in Tikrit told Xinhua.

Late on Sunday, unknown gunmen attacked a military position for the Iraqi oil infrastructure protection force in northeastern Tikrit, 170 km north of Baghdad, killing one soldier, the source said.

Meanwhile, a roadside bomb went off near a bus traveling on the main road of Dujail City, some 60 km north of Baghdad, damaging the bus and killing two people aboard, the source said.

A third roadside bomb detonated near a passing police patrol in the town of Balad, some 80 km north of Baghdad, wounding two policemen, the source added.

Salahudin province, a predominantly Sunni area, has long been the hotbed of insurgency since the U.S.-led invasion in 2003.

Source: Xinhua