Gunmen entered a mosque and murdered two Border Patrol Police (BPP) officers who were praying there, in Than To district of Yala on Friday afternoon.
Police said four armed men entered Nurul Ibadah mosque in Ban Mayo and shot both policemen in the head about 1.30pm.
The slain officers were identified as Pol Lt Adul Rakpratch and Pol Sub Lt Waesomlee Waehama, both of the 44th BPP Task Force.
It was not known what kind of firearms were used.
Police investigators reported that the gunmen mingled with local residents. The two officers were bent in prayer when the killers pulled out guns, shot them, then quickly fled.
Police blamed southern insurgents looking to cause unrest.
Pol Maj Gen Kritsada Kaewjandee, chief of Yala police, ordered an immediate manhunt for the killers.