YALA, Thailand -- Gunmen in insurgency-wracked southern Thailand killed 15 village defense volunteers and wounded five security personnel in what is believed to be the deadliest attack on government forces since the separatist rebellion began 15 years ago.

Blood-stained clothing found at the scene suggested that some of the attackers on two checkpoints in Yala province late Tuesday night also may have been wounded in exchanges of gunfire, said army spokesman Col. Kiattisak Neewong. He said four of the slain officers were women and one was a doctor.

In what appeared to be coordinated actions, nails were scattered on a highway to disable vehicles entering Yala, a small explosive device was found placed near an electrical pole to knock out power, and several burning tires were left at a school, said Col. Thaweesak Thongsongsi, a Yala police superintendent.

Thai Prime Minister Prayuth Chan-ocha said Wednesday the attack may show the insurgents are switching their focus from attacking soldiers and police to the volunteers, who are lightly armed soft targets. He said plans would have to be drawn up to better protect them.

Thailand's volunteer forces in the south are raised from villages and receive weapons training from the army but no salary. They are usually issued shotguns but often carry personal handguns, and only guard their own villages rather than seek to confront the insurgents.

More than 7,000 people have been killed since the insurgency erupted in 2004 in Thailand's three southernmost provinces of Pattani, Narathiwat and Yala, the only ones with Muslim majorities in the Buddhist-dominant country. Muslim residents have long charged that they are treated like second-class citizens, and separatist movements have been periodically active for decades. Heavy-handed crackdowns have fueled the discontent.

Police, teachers and other government representatives have often been targeted, along with Muslim residents seen as siding with the government. Buddhist monks have also been attacked. The fragmented insurgent groups have focused on vague separatist demands and have not been linked to jihadi movements.

The Thai government has been holding on-again, off-again talks with insurgents brokered by neighboring Malaysia, but factionalism among the network of rebel groups along with a disinclination by Thailand to offer any substantial concessions have stymied progress toward peace. Prayuth suggested the attacks could be meant to influence the peace talks.

Most insurgents appear to be linked to Barisan Revolusi Nasional, the most influential of the separatist groups, though local members operate with some autonomy. Generally, they stage hit-and-run attacks, such as drive-by shootings and ambushes with roadside bombs. They are also known for occasional coordinated attacks when seeking to make a political point with a show of strength.

Don Pathan, a security analyst closely watching the conflict, said the militants don't usually attack the Village Defense Volunteers, but if those units start taking an active role in chasing the insurgents, the situation could change.

Romadon Panjor, an analyst with Deep South Watch, a university-based think tank, said there have been attacks on the village defense volunteers since the system was established in 2004, but they have increased in frequency in the past one or two years as the number of self-defense forces has increased.

He said the government has felt it can shift defensive burdens to the local residents as the overall number of attacks and casualties has fallen, but as a consequence the village defense units are increasingly targeted.

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Associated Press writer Preeyapa T. Khunsong in Bangkok contributed to this report.