The attackers fled when Assam Rifles troopers rushed to the site after the post Saturday midnight attack.
The killers surrounded the camp and opened fire killing the three, Manglian, Ningboi and a woman, Harrian, a former rebel leader said.
Robert Singson, a leader of the United Tribal Liberation Army (Robert faction), said: “The number of dead would have been much higher if Assam Rifles had not come to our rescue.”
The government had allowed the UTLA(R) to open a peace panel camp in Tamenglong district to initiate the peace process. This is where the attack took place.
Two key Kuki groups have been long involved in fratricidal killings.
Singson said: “Early this year the police collected our guns meant for self protection. Since we do not have guns, the attack was carried out.”
Police have taken the bodies for post-mortem. No arrest has been made.
Chief Minister N. Biren Singh, who also holds the Home portfolio, reviewed the situation with senior police, Army and paramilitary personnel on Sunday.