Assam Rifles has charged the NSCN-IM with violating ceasefire ground rules and said cadres of the group are solely responsible for disturbing peace in Nagaland.
In a statement, the Assam Rifles said, "The faction is solely responsible for disturbing peace in the state by not observing ceasefire ground rules."
It also said that the firing at a NSCN-IM camp at Namsa-Tizit in Nagaland's Mon district and the killing a self-styled 'major' and arrest of five others on Thursday were not 'preplanned'.
"Our personnel were on routine patrol when the cadre were noticed at a camp which was not notified," the statement said.
According to the Assam Rifles, the NSCN-IM cadre fired after which its personnel retaliated.
A huge cache of arms and ammunition was recovered along with administrative stores from the camp which was a gross violation of ceasefire ground rules, it said.
Three AK-47 rifles, one two-inch mortar, two single barrel guns, two grenades, 649 rounds of AK-47 rifle, four motor bombs, 308 rounds of .303 rifle and 21 rounds of M16 rifle were seized from the militants.
The Assam Rifles also claimed that the NSCN-IM cadre were using unparliamentary and offensive language against it.
The NSCN-IM had earlier condemned the 'highhandedness' of the Assam Rifles saying, "This action of the Assam Rifles is really provocative and vitiation of the peaceful atmosphere in the area."