Army authorities have accused the Isak-Muivah faction of the National Socialist Council of Nagaland (NSCN-IM) of violating the ongoing ceasefire by moving around with weapons and gunrunning.
"The cadres (NSCN-IM) were moving with weapons outside their designated camps which is a grave violation of the ceasefire ground rules and is totally against the provisions," said an army statement issued on Thursday.
The statement comes after the killing of an NSCN-IM cadre in Assam on Wednesday in an encounter with soldiers. The NSCN-IM has a ceasefire with New Delhi since 1997 with the two sides holding peace talks to end one of South Asia's longest running tribal insurrection.
Rights groups and the NSCN-IM reacted sharply, saying the army violated the truce by killing the cadre.
But the army statement said: "When the vehicle with the miscreants was about to be checked by the security forces, the miscreants opened fire, injuring one army soldier and a civilian."
The soldiers retaliated by killing one NSCN-IM cadre and injuring two others.
"Recovery of one 9 mm sub machine gun, one 9 mm Chinese pistol and a few fired cases of AK rifle is testimony of the same and confirms the outfit's involvement in arms smuggling and trafficking to various insurgent and terrorist groups in Assam and Nagaland," the army statement said.
The charges assume significance as peace talks between NSCN-IM leaders and New Delhi are due to resume later this month.