Seven Assam Rifles personnel and one Territorial Army jawan lost their lives.
The Assam Rifles personnel also fired back and killed a militant while some others were injured in the ensuing encounter, sources added.
A water collection team comprising about 20 personnel of the Assam Rifles and the Naga Territorial Army was travelling in two vehicles from Changlangshu to Tobu in Mon district when suspected NSCN-K militants first triggered an improvised explosive device under one the vehicles and opened simultaneous fired upon the security personnel killing eight of them on the spot.
An unspecified number of security men were injured in the ambush.
There had been no attacks on security personnel since the central government initiated peace efforts in the late 1990s with the NSCN factions -- NSCN-IM, NSCN-K.
While the Centre has been talking to NSCN-IM led by Isak Swu and Th Muivah, it is yet to do so with the NSCN-K even though the outfit has been in truce.
The NSCN-K led by S S Khaplang, a Burmese-origin Naga, recently pulled out of the truce pact with the Centre.
The outfit’s headquarter is inside the jungles of Myanmar, bordering Nagaland and
Arunachal Pradesh, and has been providing training and shelter to many other insurgent groups in the region.
The NSCN-K split last year owing to sharp differences among its top rung leaders over issues related to the peace process with the central government.
A breakaway faction was formed under the leadership of Kitovi Zimomi and Khole Konyak, which favoured continuation of the peace process while the faction led by S S Khaplang went back to jungles once again breaking the truce with the Centre.