KHAR (AFP) - Two schoolboys were killed and their brother injured Wednesday when a bomb exploded in Bajaur tribal region, officials said. The trio, all brothers, were playing when the explosive device went off in Nisarabad village on the outskirts of Khar, the main town in the Bajaur tribal region, local administration chief, Adalat Khan, told AFP. Two of them, aged between nine and 11 years, were killed and their 13-year-old brother wounded, he said. They were school students, he said. A security official confirmed the casualties, saying that it was unclear if the bomb was planted by militants or was left during a six-month battle fought between government forces and insurgents.