Four people were killed and 20 others injured in five bomb explosions on houses in and near the Sunni city of Fallujah in Iraq's western province of Anbar on Monday, a provincial police source said.

Unknown armed men planted bombs in four houses in Fallujah, some 50 km west of Baghdad, and in a fifth house at a village on hte outskirts of the city, the source told Xinhua on condition of anonymity.

The blasts on early Monday morning targeted the houses owned by families who have sons working for Iraqi security forces, the source said.

The blasts destroyed the houses and caused damages to several nearby houses, the source added.

The Iraqi security forces sealed off the scene as dozens of policemen and soldiers were deployed on the main streets and intersections, he added.

Insurgent attacks continue in the once volatile province of Anbar, which has been relatively calm for more than two years after Sunni tribes and anti-U.S. insurgent groups turned to cooperate with the U.S. troops and Iraqi security forces against al-Qaida network in Iraq.