Twenty-one militants were killed in air strikes and ground operation in Pakistan's North Waziristan on Tuesday, the military’s media wing Inter Services Public Relations said.“Combined strikes by PAF, the army and ground forces continued the hunt for fleeing terrorists through a chase and cordon operation,” Inter Services Public Relations director general Lt. Gen. Asim Bajwa said.Bajwa confirmed that “21 terrorists were killed last night as operations continue". He said, "Important heights and passes along the Pakistan-Afghan border have been secured. The Shawal Valley sanitisation is in progress.”The Pakistan Army launched a ground offensive in North Waziristan Agency’s mountainous Shawal Valley at the end of last year. The valley was regarded as the last haven of fleeing homegrown militants and their foreign cohorts.The operation was aimed at clearing Taliban and Al Qaeda strongholds in North Waziristan and claims to have killed more than 3,750 militants since it commenced in 2014.Since last year, the military stepped up operations in the deeply forested ravines of the valley - which straddles North and South Waziristan agencies along the border with Afghanistan - and softened militant targets in the valley through continued airstrikes.