The unit was returning home after providing security to Buddhist devotees and monks at a temple in the evening of Maka Puja Day when the explosion occurred at 10.40pm.
The explosion occurred on a road along the railway in Yaba village in Tambon Rusoh in Rusoh district.
Police said insurgents detonated the home-made bomb with a wired control. Police said a wire, which was more than 100-metres long, was found at the scene.
Sgt Dejpol Lowannee, the chief of the patrol unit, Cpl Sompong Taesanan, Pvt Kamol Panthong, and Pvt Suwat Nilpak were killed. Pvt Suriya Jachalee was severely injured and rushed to the Rusoh Hospital.
The blast reduced the vehicle in which the five soldiers riding to pieces, which were scattered over a radius of 4 metres. The blast also made a hole one metre deep and three metres wide hole in the road.
Police said the unit was returning to base in two vehicles after being deployed to keep security at the Rat Samosorn Temple where Buddhists came out to celebrate the Maka Puja Day.