BANGKOK (Reuters) - Suspected separatist insurgents stormed a security checkpoint in Thailand’s Muslim-majority south and killed at least 15 people, including a police officer and many village defense volunteers, security officials said on Wednesday.

It was the worst single attack in years in a restive region where a long-running Muslim insurgency has killed thousands of people in a fight against central government rule in overwhelmingly Buddhist Thailand.

The attackers, in the province of Yala, also used explosives and scattered nails on roads to delay pursuers late on Tuesday night.

“This is likely the work of the insurgents,” Colonel Pramote Prom-in, a military regional security spokesman, told Reuters. “This is one of the biggest attack in recent times.”

There was no immediate claim of responsibility, as is common with such attacks in the region.

A decade-old separatist insurgency in predominantly Buddhist Thailand’s largely ethnic Malay-Muslim provinces of Yala, Pattani, and Narathiwat has killed nearly 7,000 people since 2004, says Deep South Watch, a group that monitors the violence.

Many of the dead at the checkpoint were members of the Village Defence Volunteers, a community-watch type organization, who were believed to be giving information to the local police and military.

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“Normally the insurgents don’t hit these village volunteers because they are considered civilians, unless they crosses the line and become part of state apparatus,” Don Pathan, an expert on Thailand’s deep south, told Reuters.

The population of the provinces, which belonged to an independent Malay Muslim sultanate before Thailand annexed them in 1909, is 80 percent Muslim, while the rest of the country is overwhelmingly Buddhist.

Some rebel groups in the south have said they are fighting to establish an independent state.

Authorities arrested several suspects from the region in August over a series of small bombs detonated in Bangkok, the capital, although they have not directly blamed any insurgent group.

The main insurgency group, the Barisan Revolusi Nasional (BRN), denied responsibility for the Bangkok bombings, which wounded four people.

In August, the group told Reuters it had held a secret preliminary meeting with the government, but any step toward a peace process appeared to wither after the deputy prime minister rejected a key demand for the release of prisoners.