An accumulation of methane gas apparently caused the explosion , the governor of the Colombian state of North Santander told the radio service . NEW : A Colombian mining agency says six miners are dead . NEW : The agency says 20 miners were injured . The blast happened near Venezuela 's border with Colombia . A build-up of methane gas may be to blame , governor says .
NEW : A Colombian mining agency says six miners are dead . NEW : The agency says 20 miners were injured . The blast happened near Venezuela 's border with Colombia . A build-up of methane gas may be to blame , governor says .