At least three troopers were killed and six injured on Wednesday when Maoists exploded a landmine in Odisha's Malkangiri district, police sources said.The incident occurred near Sarjubandh in Chitrakonda in the district when the Border Security Force (BSF) personnel accidentally stepped on the landmine planted by the Maoists.The troopers were returning to their base camp at Chitrakonda after a combing operation.The injured were shifted to Malkangiri district headquarter hospital.After the incident, senior security officials rushed to spot and the search and combing operation was intensified in the area.