Two soldiers and a local government official were killed early on Tuesday when a roadside bomb exploded near their vehicle in Thailand's insurgency-hit Muslim south, police said.
The three were travelling to investigate an arson attack at a school in Pattani province when the bomb exploded, police said.
The victims -- all in their 40s -- were a Pattani district leader, a senior soldier with the provincial security force and an army ranger, police added.
The attack was the bloodiest in a series of five bombings and two arson attacks early on Tuesday in Pattani, one of three provinces along the Malaysian border that has been hit by three years of separatist unrest.
No injuries were reported in the other attacks.
More than 2,200 people have been killed and thousands more wounded in separatist violence that erupted in the south in January 2004.
The violence has escalated sharply this year despite a series of peace initiatives by the army-installed government.
Prime Minister Surayud Chulanont insisted on Monday that secret talks aimed at quelling the unrest were progressing. A security official said the government was in contact with a separatist leader believed to be in Qatar.