In Salahudin province, a fierce clash erupted when gunmen attacked an Iraqi army checkpoint in western the city of Baiji, some 220 km north of Baghdad, leaving two soldiers and four gunmen killed, a provincial police source told Xinhua on condition of anonymity.
One of the killed attackers was later identified as a local leader of al-Qaida militant group in the city, the source said.
Salahudin is a Sunni-dominated province. Its capital Tikrit, about 170 km north of Baghdad, is the hometown of former President Saddam Hussein.
In a separate incident, a civilian was killed and nine others wounded when one of eight mortar rounds, apparently targeting a nearby army base, missed its target and landed on their house outside the town of Hamam al-Alil south of Nineveh's provincial capital city of Mosul, some 400 km north of Baghdad, a provincial police source anonymously told Xinhua.
It was not immediately known whether the mortar barrage on the military base caused any casualty, the source said.
Separately, a policeman was wounded when gunmen blew up four improvised explosive devices planted in a watching tower of a joint police and army checkpoint in al-Jamia district in the northeastern part of Mosul, the source added.
Iraq is witnessing its worst eruption of violence in five years, raising fears that the latest bloodshed is sliding the country back toward a full-blown civil conflict that peaked in 2006 and 2007, when the monthly death toll sometimes exceeded 3,000.