The casualties were identified as paramilitary ranger volunteers Adul Rattanasuanjit and Artit Kamjan and two members of a village protection unit--Arring Dasaw and Usree Uma, said Pol Sub-Lt Thanin Kanthai of Chanae police station.
All the victims were taken to Chanae Hospital for medical treatment.
Paramilitary Ranger Adul was severely injured and was later transferred to Naradhiwasrajanagarindra Hospital.
According to the initial investigation, while six rangers and a group of village volunteers were on patrol, providing security in the area, they were directed to inspect a suspicious object later identified as a decoy explosive device, at the home of the Dusongyo village head.
On the way a bomb hidden at a roadside area was triggered by remote control, wounding the four men.
The explosion caused a two-foot deep and three-foot wide hole in the roadway with bomb fragments scattered around the area.
Police believed that insurgents intended to ambush the security team.