BAGHDAD — Bombs and gunmen killed six people in Iraq on Sunday, four of them from the same family, security sources said.

The four family members -- parents and two daughters in their 20s -- were all shot in the head overnight by gunmen who spared a third, seven-year-old daughter, interior ministry and security officials said.

"This was probably a terrorist crime, which we are investigating," said Baghdad security spokesman Major General Qassim Atta.

Also on Sunday, magnetic "sticky bombs" attached to cars killed two civilians and wounded another in Kirkuk, a violence-prone, religiously and ethnically diverse northern province, senior police officials said.

In the western part of Kirkuk, police said they found the corpse of the leader of an anti-Al-Qaeda militia who was kidnapped a week ago. It was unclear when he was slain.

Violence has sharply fallen in Iraq since its peak during sectarian killings of 2006 and 2007, but bombings, shootings and kidnappings remain common.

The UN envoy to Iraq, Ad Melkert, said this month that violent incidents still occur on average 25 times per day although the number was "a lot lower than what it used to be."