At least six militants and two security personnel, including a lieutenant colonel were killed in a clash with militants in the northern tribal region of Pakistan, the military’s media wing reported on Monday.The Inter-Services Public Relations (ISPR) confirmed the killings in the clash that took place in Shawal area of North Waziristan.The final phase of the Zarb-i-Azb operation in North Waziristan got under way on Thursday as troops launched a ground offensive in Shawal Valley, one of the last strongholds of militants in the region. "we have moved into the last stage of the operation."The ground action in Shawal has commenced," military spokesman Maj. Gen. Asim Bajwa told Dawn.The Zarb-i-Azb operation began in June last year and the army said it has cleared most of North Waziristan.