The three NSCN(K) cadre were at a liquor joint in New Market area when they were gunned down at close range, the sources said.
Although the identity of the attackers was yet to be ascertained, the police suspected that the case was an incident of underground group rivalry.
There have been reports of intermittent armed clashes between NSCN(K) led by S S Khaplang and Khole-Kitovi led GPRN/NSCN in different parts of the state for past couple of months.