IMPHAL, April 26 ? Four children were killed and four others injured when a bomb exploded inside a school compound in Manipur today, official sources said, reports PTI. The bomb, planted by unknown persons, went off at 11.40 am at a school compound at Hangeipat area under Saikul police station in Senapati district killing four children on the spot. Four others sustained grievous injuries, sources said. They were admitted to J N Hospital here while the bodies were sent for post mortem. Police launched a combing operation to find out the culprits but no arrest was made so far.