The three NSCN(K) cadre were at a liquor joint in New Market area when they were gunned down from close range, they said.
Although the identity of the attackers was not known, the police suspected it to be a case 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.