Police said the explosion occurred at 10.55am at Taloh village in Tambon Sakor of Narathiwat’s Si Sakhon district.
The five rangers were building a house for villagers and the insurgents apparently remotely detonated a homemade bomb planted in the middle of the house, police said.
The ranger killed in the blast was identified as Udomsak Raotapong.
The injured were rushed to a nearby hospital.