A powerful explosion in a house in west Baghdad killed at least 29 people and wounded 18, police said Wednesday. They said the attack was an ambush staged by insurgents. Police patrols were en route to a raid in Baghdad's Ghazaliya neighborhood late Tuesday after an anonymous call tipped them about a suspected militant hideout in the neighborhood, an official in Ghazaliya police station said. As they were about to enter the house, an explosion erupted from inside, he added. At least 29 people were killed, including 7 policemen, and 18 others were injured. Six houses collapsed in the blast and several people are believed to be still trapped underneath the rubble. The police official said the attack was "evidently an ambush" and that "massive amounts of explosives" were used.