A bomb exploded under a truck escorting teachers to work in the province of Yala on Tuesday, immediately killing one officer, police said.
Insurgents then shot and killed a further four officers who had survived the initial blast.
A second bomb exploded nearby moments later. Police Colonel Jirasak Wikraicharoenying said that explosion was meant to prevent security forces from rescuing the men.
A third device also exploded outside the home of a local government official in neighbouring Narathiwat province, but injured no one.
Students in Narathiwat found a fourth bomb outside a school as they were arriving for their classes, but police managed to defuse it.
Islamists single out schools and their teachers as symbols of the predominantly Buddhist central government.
Two villagers were killed in separate attacks on Tuesday in Narathiwat by gunmen riding behind drivers on motorcycles, police said.
The three southernmost provinces of Yala, Pattani and Narathiwat have been hit by almost daily bomb and gun attacks in a renewed separatist insurgency in which more than 1,300 people have been killed since January 2004.