Gunmen attacked a police checkpoint north of the Iraqi capital on Tuesday, killing seven including a captain, a police officer and a doctor said.
The attack took place on the highway north of the city of Samarra, the sources said.
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Iraqi security forces are often targeted by militant groups opposed to the government.
Violence in Iraq has reached a level not seen since 2008, when the country was just emerging from a brutal period of sectarian killings.
It took just five days for this month's death toll to surpass that for all of January last year.