BANGKOK • Three police officers have been killed by a bomb buried beneath a road in Thailand's southernmost Yala province, where Muslim separatists have been waging a simmering insurgency against the state, the authorities said.

The police were travelling in two pick-up trucks yesterday when the first was blown up by a roadside bomb, said police Lieutenant-Colonel Chamnan Bhutpakdee.

"The assailants detonated the bomb when the truck was passing over, instantly killing the three officers," he said. Insurgents then opened fire on the second vehicle, wounding two officers. One was in critical condition.

The three dead officers were in their late 20s and "were on a trip to gather intelligence", said a police officer in Krong Pinang district.

Remote and surrounded by densely forested hills, Krong Pinang is an insurgency hot spot where mistrust of Thai security forces runs high.

Yala, along with Pattani and Narathiwat, are Muslim-majority provinces in the deep south of mostly-Buddhist Thailand. Insurgency has plagued the region for decades. Since 2004, more than 6,500 have been killed, according to the Deep South Watch monitoring group.

The rebels are widely believed to be behind an unprecedented string of bomb blasts on tourist towns outside their conflict zone in August, killing four people. But the Thai authorities have avoided linking those attacks to southern militants.

AGENCE FRANCE-PRESSE, REUTERS