Five policemen were killed on Tuesday when unknown militants opened fire on a police vehicle in Pakistan's northwestern Khyber Pakhtunkhwa province, police sources said.The incident happened at about 8:45 a.m. local time (0345 GMT) when assailants began firing on the vehicle in Karak district, the sources told Xinhua on condition of anonymity.Police returned fire immediately, triggering a gun battle that continued for around an hour.All five police personnel on board the vehicle were killed during the exchange of fire, the sources said.After the attack, the militants also set the police vehicle on fire before fleeing the scene, the sources added.No...