BANNU : Three students were injured when an explosive device went off inside the classroom of a government school in district Bannu on Monday. Police said the explosive device was brought by a student namely Suleman of grade-1X, resident of Frontier Region, for sale and when he took out the device from his bag and showed it to his fellow, the grenade suddenly exploded, causing injuries to three students. The injured students were identified as Suleman, Arsalan and Asad Akhtar.