Twenty-five people were killed and 23 wounded in separate attacks mainly targeting Iraqi security forces across Iraq on Tuesday, police said.

In Iraq's northern province of Salahudin, a suicide bomber drove his explosive-laden car into an army checkpoint in north the provincial capital city of Tikrit, killing five soldiers and wounding five others, a provincial police source told Xinhua on condition of anonymity.

The blast destroyed two police vehicles and also damaged several nearby civilian cars, the source said.

In Anbar province, an army commando force clashed with gunmen suspected to be linked to al-Qaida militant group, in the town of al-Garma, east of the city of Fallujah, killing 12 gunmen, a provincial police source said anonymously.

Separately, artillery and mortar shelling on several neighborhoods in the besieged city of Fallujah left two people killed and four others wounded, a medical source from the city hospital said.

In Baghdad, seven people were wounded in a bomb explosion at a marketplace in Sabie al-Bour area, north of the capital, a police source said.

In northern Iraq, gunmen shot dead a policeman in front of a police station in the city of Mosul, some 400 km north of Baghdad, and then police chased with the attackers and killed one of them, a local police source said.

In a separate incident, an army force carried out a search operation at a neighborhood in Mosul and clashed with gunmen, killing two of them and arrested five suspects, the source added.

Also in Mosul, a soldier was gunned down by a sniper, while a policeman was killed and four others injured in the city, the source said.

In addition, an intelligence officer and two policemen were wounded when gunmen fired at them in the city of al-Ba'aj, some 120 km west of Mosul, a local police source said.

Iraq is witnessing its worst violence in recent years. According to the UN Assistance Mission for Iraq, a total of 8,868 Iraqis, including 7,818 civilians and civilian police personnel, were killed in 2013, the highest annual death toll in years.