Six family members were killed and four others injured when a hand grenade exploded on board a pick-up truck in a Pakistani tribal area near the Afghan border, officials said Sunday. The incident took place late Saturday near Asar Madakhel village, around 45 kilometres (22 miles) west of Miranshah, the main town of the restive North Waziristan tribal district. "I saw the bodies of a husband, wife and their four children, and also four injured at the hospital," local administration official Niaz Gul said. Gul said the pick-up carrying passengers from the border village of Lawara Mandi was heading to Miranshah when the grenade exploded. "It is not clear how the grenade exploded," he said, but added that tribesmen usually carried guns and hand grenades with them. A tribesman injured in the blast told AFP that some of the passengers were carrying guns and hand grenades, but that he did not know how the grenade exploded. "We were travelling and suddenly there was blast," Mir Aslam Khan said.