"Initial investigations showed that it was an attack by Muslim insurgents," Thammasak said.
The attack took place in Sabayoi, a predominantly Muslim district, next to Pattani province, which along with Yala and Narathiwat provinces has been the scene of an uprising that has led to more than 1,900 deaths in the past three years.
A Muslim man in Yala, a Buddhist man in Pattani and a Buddhist couple in Songkhla were killed over the weekend.
In Pattani on Monday, a group of 70 Muslim women along with their children gathered in front of a police station in Nong Chik district to demand the release of Manadee Samah, a suspected Muslim fighter who was arrested on Sunday.
No violence was reported.
Surayud Chulanont, the prime minister, has pledged to end the violence and upon his appointment as premier, he offered an apology to local Muslims for past government wrongdoing.
But his visit to the region on Saturday – in which he reiterated his commitment to forging a peaceful solution to the unrest – coincided with the ambushing of police patrols and torching of a government school by the suspected fighters.