Two children were killed and six others were injured as an explosive device left over from the wars exploded in Nangarhar province Friday, a local official said. \"The tragic incident occurred at 11:00 a.m. local time today in Behsoud district when the children were playing on a ground and suddenly an explosive device, left over from the past wars went off and killed two innocent children on the spot,\" Nimatullah Khan the governor of Behsoud district told Xinhua. Six more children were injured in the blast, he added. Afghanistan is one of the most mine-contaminated countries in the world as thousands of mines and explosive devices left over from the past wars and conflicts often kill and maim innocent people mostly children.