Four CRPF jawans were killed and nine others were injured in an ambush at Keithelmanbi in Senapati district on Wednesday, official sources said.
The militants, who were hiding by the roadside, fired at the convoy of 143th battalion of CRPF with automatic weapons when they reached the hilly Keithelmanbi area.
The militants also exploded grenades at the three vehicles of the security personnel before firing, the sources said.
It was yet to be ascertained which insurgent outfit was behind the ambush.
The CRPF personnel who were returning to their camp at Lamphel area in Imphal from Kotlen via Keithelmani, retaliated and the exchange of fire lasted more than two hours, sources said.
In the gun battle, at least 13 CRPF personnel sustained injuries. Of them, four died on the way to and in hospital.
The bodies were kept at the Regional Institute of Medical Science and Hospital for post mortem.
The condition of the injured, being treated in the same hospital, was stated to be serious.
Casualty, if any, on the side of the militants was not immediately known.
On Sunday, militants of the banned People's Revolutionary Party of Kangleipak (Prepak) had attacked a group of Assam Rifles personnel killing one jawan and injuring another at Umathel area in interior Thoubal district.
Official reports said angry Assam Rifles personnel had beaten up about 45 villagers including women of Umathel after the ambush.