Three Border Security Force (BSF) personnel were shot dead by Separatist guerrillas in Dhalai district of Tripura on Saturday.
A lobourer was also killed in the same incident.
"The BSF men (77 Battalion) were guarding those working on the India-Bangladesh border fencing being constructed by NPCC when they got ambushed," police spokesman Mayajoy Rupini said.
The dead worker belonged to the National Project Construction Co (NPCC).
The police has blamed the National Liberation Front of Tripura (NLFT) for the killings.