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.
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.