At least 25 militants, including three key commanders, were killed in clashes with security forces in North Waziristan region of Pakistan on Wednesday.According to sources, the ground operation was carried out in Shawal Tehsil where three militant commanders of the Tehreek-e-Taliban Pakistan were also eliminated, Geo News reported.The Pakistan Army launched Zarb-e-Azb, a comprehensive anti-militant operation, in 2014 against foreign and local terrorists who were hiding in sanctuaries in the North Waziristan tribal region. The operation was launched a week after a brazen insurgent attack on the country's busiest airport in Karachi.The tribal region, which borders Afghanistan, has been used as a base by militants over the years.