At least four persons were killed and three sustained injuries in a fierce clash between the militant groups in Tehsil Shawal of North Waziristan Agency (NWA), (Geo News) reported Tuesday. Official sources said that two groups of militants went on a fierce clash late last night at Taunda Darra in Tehsil Shawal of NWA, leaving four killed and three injured. Following the incident, the militants fled away towards nearby mountains.