A suicide bomber detonated a car packed with explosives at an Iraqi army checkpoint north of Baghdad on Tuesday, killing at least three people, police said.
The blast in Taji, 20 km (12 miles) north of the capital, followed another suicide attack in the same town a day earlier that killed at least 22 people.
It was the eighth suicide bombing in a month in Iraq, indicating insurgents are intent on stepping up violence a year after U.S. troops pulled out of the country, where Shi'ite, Sunni and ethnic Kurdish factions still struggle over how to share power.
The Shi'ite prime minister has been struggling to quell mass protests by Sunni Muslims against what they see as the marginalisation of their sect since the fall of Saddam Hussein and the empowerment of Iraq's Shi'ite majority through the ballot box.
Violence has fallen from the height of the sectarian slaughter that killed tens of thousands in 2006-2007, but insurgents have still been carrying out at least one major attack a month since U.S. troops withdrew in December 2011.
Unrest in Iraq's Sunni heartland is compounding fears the war in neighbouring Syria - where Sunni rebels are battling President Bashar al-Assad, an ally of Shi'ite Iran - could upset Iraq's own delicate sectarian and ethnic balance.