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BANGKOK (Reuters) - A roadside bomb planted by suspected Muslim insurgents killed four army rangers and wounded six, including a civilian, in southern Thailand on Friday, a security official said.

A decades old-separatist insurgency in predominantly Buddhist Thailand’s largely Muslim provinces of Yala, Pattani, and Narathiwat has killed more than 6,500 people since 2004.

The bomb was planted under a road that was being built in Pattani, the security official said.

“The group that planted the bomb is using old techniques in order to create instability in the region. They planted the bomb under a road currently under construction,” said Pramote Prom-in, a spokesman for security forces in the region.

Friday’s blast followed roadside bombs last week that killed two soldiers and wounded more than 20 people in Yala.

There was no claim of responsibility for the blast, which is usually the case in Thailand’s deep south, where insurgents are fighting for secession.

Thailand’s three southernmost provinces were part of an independent Malay Muslim sultanate until they were annexed in 1909.