Clashes erupted when militants attacked anti-al-Qaeda fighters at a checkpoint on the highway between Tuz Khurmatu and Tikrit on Monday. Three fighters and two militants were killed as a result.
Al-Qaeda-linked militants frequently target the Sunni militiamen who are against insurgency in Iraq.
With the latest violence, over 165 people have been killed in attacks in the first eight days of July -- far more than in the whole month of December, AFP reported.
Iraq has seen a surge in violence since the beginning of the year.
Last year, a total of 4,471 people were killed in militant attacks nationwide.
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