Three Thai policemen were killed and one was seriously injured in a bomb attack in the latest violence in a five year separatist rebellion in the south of the country, police said on Thursday.
The 20 kg (44 lb) bomb was buried along a rural road in Nongjik in Pattani, one of three far south provinces where more than 3,000 people have been killed since the violence erupted in 2004.
"One of those three was a deputy superintendent of Nongjik police station. They were killed while they were guarding teachers on the school bus," a police official said.
The rebels have never revealed themselves publicly or claimed responsibility for the violence, which has remained limited to the rubber producing region abutting the Malaysian border.
It was a Muslim sultanate until annexed by predominantly Buddhist Thailand a century ago. The majority of the population is Muslim and Malay speaking, with few links to the rest of Thailand.
In an incident earlier this month, two paramilitary rangers were shot dead and decapitated in the region.