The militant was identified as 'commanding officer' of NDFB (Songbijit) Jwrimiya Muchahary alias M Jwrimin.
Based on specific intelligence about presence of a terrorist camp in the area, a search operation was launched jointly by the Army's Red Horn Division under the Gajraj Corps and state police and they found the camp.
Finding the securitymen, the militant fired towards them who retaliated in which the extremist got killed, the spokesman said.
Muchahary was self styled commanding officer of 3rd battalion of NDFB(S) and it was also likely that he was recently appointed as the 'deputy commander-in-chief of NDFB(S), the spokesman said.
He was involved in the adavasi massacre of December 23, 2014 at Dwimuguri village of Chirang district in which over 70 persons were killed, he said adding that he was also involved in the killing of a teenaged girl of the village in August that year on suspicion of being a police informer.