Four of a family were killed when unknown culprits attacked a house with hand grenade here late Saturday night. According to details, unidentified accused hurled hand grenade at a residential house in Kot Khadak of Tank. As a result of the attack, house owner Salahuddin, his two sons and a nephew were killed on the spot. Heavy contingent of police reached the scene and after shifting the bodies to District Headquarters (DHQ) Hospital started investigations.