ISLAMABAD: Six persons were killed while three other received serious bullet injuries as two groups opened firing on each other near the area of Naushahro Feroz in Nawabshah on Tuesday. According to police sources the ill-fatted incident occurred as two rivalry groups fought over an old enmity, a private news channel reported. The bodies and injured were shifted to a nearby hospital for medico-legal assistance, they stated. Police had registered an FIR against the murderers and started search operation to arrest the culprits involved in the incident, they further informed.