At least fifteen people were killed and another four injured in attacks by suspected Muslim rebels in Thailand’s violence-wracked south, an army spokesman said on Wenesday, the largest death toll in years.

The Malay-Muslim south has been in the grip of a bloody insurgency that has killed more than 7,000 people over the last 15 years.

Late Tuesday militants struck two checkpoints in Yala province manned by civil defence volunteers, opening fire on them as a group of villagers stopped to talk, southern army spokesman Pramote Prom-in told AFP.

“Twelve were killed at the scene, two more (died) at the hospital, and one died this morning,” said Pramote, adding that the rebels took M-16 rifles and shotguns from the checkpoints.

The areas surrounding the checkpoints have been closed off and are currently under forensic investigation, he said.

Rebels seeking autonomy for the culturally distinct region bordering Malaysia have been fighting the Buddhist-majority Thai state, which colonised the area over a century ago.

The grinding conflict is characterised by tit-for-tat attacks that usually target symbols of the Thai state and its security forces but civilians from both Muslim and Buddhist communities often get caught in the crossfire.

Tuesday’s attack marked the largest coordinated effort “in a very long time”, said Don Pathan, an expert on the so-called “deep south”.

The incidents have been fewer in recent years, but the hits have been “more intense”.

“It is a reminder that they are still here,” Pathan said.

The rebels accuse the state of railroading their distinct culture as well as carrying out routine abuses which go unpunished.

Tuesday’s violence comes months after the death of a Muslim man, Abdulloh Esormusor, who was left in a coma after being interrogated at a notorious Thai detention centre.

Suspects are routinely taken for interrogation and held under emergency laws in detention centres where rights groups have documented torture.

Days after Abdulloh’s detention, four people were killed in a late-night attack on a military outpost, fuelling speculation of a retaliatory operation.

A week later several small bombs exploded in Bangkok, injuring four people as the city hosted a major summit attended by top diplomats, including US secretary of state Mike Pompeo.

Thailand has linked the bombs to southern insurgents and said the devices used were similar to those found in the south — though no group ever claimed responsibility in the attacks.