Pol Lt Jaruek Pathompong of the Pakchong police station said the explosion occurred at 9:5 am, shortly after workers found the bomb and took it to be kept at the back of their pick-up truck.
The workers were installing tap water pipes along the old Mittraparp Road in Tambon Nong Sarai in Pak Chong district.
A worker died at the scene while another was pronounced dead at the district hospital. The worker, who died at the hospital, was identified at Sompong Taothong, 36. The other remained unidentified.