MOSUL— Militants ambushed a minibus carrying Iraqi soldiers and in a separate attack opened fire on a checkpoint in the north of the country, killing at least 13 people in total on Wednesday, police said.
Nine policemen were killed in the checkpoint attack, which took place in Shura, 50 km (35 miles) south of Mosul, Iraq's third largest city and capital of the Sunni-dominated Nineveh province.
Separately, gunmen ambushed a minibus on the road to Mosul from Baghdad, shooting dead four soldiers in western Tikrit, 150 km (95 miles) north of the Iraqi capital.
Sunni Islamist militants have been regaining momentum in their insurgency against the Shi'ite-led government in recent months, striking on an almost daily basis.
Iraq's steadily deteriorating security was highlighted by a mass jailbreak near the capital on Sunday when around 500 convicts, including senior al-Qaida operatives, escaped after militants attacked two prisons.
The Islamic State of Iraq and the Levant, which was formed through a merger between al-Qaida's Syrian and Iraqi branches, claimed responsibility for the raids and said it had freed its jailed comrades after months of preparation.
One security official told Reuters on Tuesday that some of the escaped inmates were heading to Syria to join the ranks of the mainly Sunni rebels fighting to overthrow President Bashar al-Assad, whose Alawite sect derives from Shi'ite Islam.
Sectarian tensions across the region have been inflamed by the Syrian civil war, which has also drawn in Shi'ite fighters from Iraq.
Insurgents have been recruiting from the country's Sunni minority, which increasingly resents Shi'ite domination since the U.S.-led invasion that toppled dictator Saddam Hussein in 2003.
More than 720 people have been killed in militant attacks in Iraq so far in July, according to violence monitoring group Iraq Body Count.
Three roadside bombs in the volatile, ethnically mixed city of Kirkuk left several people wounded and a car bomb explosion near a market in the town of Tuz Khurmato injured a further three.
Recent attacks in Iraq: