The operation to flush out terrorists from the dense forest area in Anantnag district entered into its fourth day as drones and helicopters were pressed into service to track and neutralise the ultras who killed three security forces officers, officials said on Saturday. The security forces fired several mortar shells towards the forest, they said. Major Ashish Dhonchak, 19 Rashtriya Rifles Commanding Officer Col Manpreet Singh, Deputy Superintendent of Jammu and Kashmir Police Humayun Bhat, and a soldier were martyred  in the encounter with the militants on Wednesday.