SABAYOI, Thailand — Attackers hurled explosives and opened fire on an Islamic school in southern Thailand, killing three students and sparking a riot by angry Muslim villagers, officials said yesterday.

Shortly after the attack, three Buddhists were shot dead in the same district, raising fears that a festering insurgency that has already taken more than 2,000 lives could erupt into open combat between the Islamic and Buddhist communities.

The Bamrungsart Pondok boarding school was attacked Saturday evening as 75 boys were sleeping. Attackers lobbed explosives and sprayed dozens of bullets into a dormitory, killing a 12-year-old and two 14-year-olds, police Colonel Thammasak Wasaksiri said.

Seven other teenagers were wounded in the attack in the Sabayoi district of Songkhla province, he said.

An estimated 500 protesters gathered outside the school yesterday, carrying the dead children’s bodies through the crowd and setting fire to two buildings at a nearby government-owned school. Some hurled stones at police during the protest, which lasted several hours until a local Islamic leader persuaded the crowd to disperse peacefully, a provincial police chief, Major General Paithoon Pattanasophon, said.

General Thammasak said police believe Islamic insurgents staged the school attack in an attempt to convince villagers that authorities were responsible and win them over to the insurgents’ cause. Villagers, however, refused to believe Muslims were behind the violence and blamed government security forces, he said.

Thai authorities also blamed insurgents for a bombing at a mosque and a grenade attack at a tea shop last Wednesday that killed two Muslims in neighboring Yala province. Those attacks came hours after suspected Islamic insurgents killed eight Buddhist passengers in a commuter van in the same district of Yala, shooting them in the head execution-style.

After the school attack, suspected Islamic insurgents stormed a nearby charcoal factory yesterday, killing two Buddhist employees and wounding at least two others. Separately, a Buddhist man riding a motorcycle was gunned down.

Thailand is overwhelmingly Buddhist, but the country’s far South is predominantly Islamic, and residents of the region have long felt that they are treated like second-class citizens. The southern Islamic provinces have hundreds of religious Islamic schools, and authorities have accused some of them of harboring insurgents and serving as a training ground for violence.

Lieutenant General Wirot Buacharun, the army commander in charge of the restive provinces, said security forces had recently raided an Islamic school and confiscated an M-16 assault rifle, bullets, a computer containing suspicious material, and other documents believed to be linked to the insurgency.