Intelligence inputs suggest that Army's continued operations in difficult and inaccessible jungles of Chirang District in Assam have forced the NDFB-S terrorists to flee from their hideouts.
The operation was intensified after over 70 people were killed in various attacks by NDFB-S last year.
The Army has apprehended or neutralised several members of the insurgent group.
"Due to this fact, the NDFB-S has aligned itself with UNLFW, an umbrella organisation of North East terrorist groups, which is likely to boost the group's sustenance," army sources said.
The army had this week arrested a top member of NDFB-S Central Council from Tukrajhar, Chirang District, in a joint operation with Assam police.
The individual, who was identified as Sumanta Basumatary was the Joint Secretary (Home) of newly-formed Central Council of NDFB-S and a Bhutan-trained terrorist.
The Central Council has 23 members. His responsibility included coordination of terrorist activities, internal discipline, media interaction and propaganda, the sources said.
Basumatary was very close to the outfit's new Vice President G Bidai and is believed to be the "brain" behind the killing of adivasis on December 23, 2014 in Kokrajhar district.
Thereafter, he fled to Bangalore and had recently returned to Chirang, the sources said, adding his arrest is a major blow to NDFB-S.
Follwing his arrest, the army had also apprehended a female cadre of the group.