At least 18 militants have been killed while three soldiers were martyred in last 24 hours of ongoing military operation in northwestern parts of the country, report said. The militants were killed in various areas of Swat and Dir where the security forces were engaged in clearance and search operation, says a handout issued by the ISPR here Tuesday. Forces have also apprehended 23 terrorists during the operation, it added. In Swat, three soldiers were martyred while six others, including three officers, were injured in a clash with militants at Shah Dherai area of Swat -- the last stronghold of the militants in the district. Eight militants were killed in shootouts with forces in Matta and Beha valley.