Yala provincial police were alerted at about 6am and rushed to the scene at Than Nampheung school in the Yala provincial seat. Responding firefighters put out the blaze of the red Toyota Mighty X pickup.
Four bodies, the three volunteers from the 41th regiment based in Yala's Raman district and a housemaid working for the 41th regiment were found near the vehicle.
About one hundred M16, AK47, 9mm and shotgun cartridges were found scattered on the road.
A ranger who witnessed the incident told police that he had driven his motorcycle from the base, accompanying the four victims to market to buy food.
He was a half kilometre ahead of his companions and found many triangle spikes on the road in front of Than Nampheung Shool. He turned back to warn his friends, but heard shots before arriving at their vehicle.
He found that his companions and the base housemaid were killed and the truck was burning.
Police believe there were at least five insurgents involved in the attack, possibly hidden at the roadside bush before the attack.
Weapons belonging to the victims were carried away by the assailants before they set fire to the truck.