Suspected Muslim insurgents hurled a bomb to stop a commuter van in Thailand's restive south Wednesday, then shot its nine Buddhist passengers execution-style, killing eight of them, military and hospital officials said.

The cold-blooded attack came after officials announced they were stepping up security in the south, where a Muslim insurgency has claimed more than 2,000 lives since 2004.

Suspected insurgents bombed the van as it slowed into a curve in the road, which they had also blocked with a large tree trunk, said police Lt. Kitti Mankhong, a duty officer in the Yaha district of Yala province, where the attack occurred.

Armed with assault rifles, the attackers first shot at the driver and then opened the side door of the van and fired at each of the passengers, he said. The Muslim driver, who was hospitalized with a gunshot wound to the face, survived the morning attack, as did one passenger.

"Everyone was shot in the head at close range, execution style," Kitti said.

A Buddhist woman who survived the shooting was hospitalized in critical condition. Police had earlier said all nine passengers had been killed, but a statement from the army later said eight were dead.

The van was shuttling people from the Betong district of Yala province to Hat Yai, the south's major city, in the neighboring province of Songkhla.

Police and soldiers were searching for the attackers, he said.

The attack came as authorities beefed up security for the Tuesday anniversary of the founding of the Barisan Revolusi Nasional, or National Revolution Front separatist group. Police had warned that insurgents might try to mark the anniversary with violence.

The BRN was formed in 1963, partly in opposition to the Thai government's policy at the time of forcing southern Muslims to assimilate into predominantly Buddhist Thai society. The government later changed the policy.

Military officials believed that BRN-Coordinate, a BRN offshoot, has played a vital role in the current violence.

Gen. Montree Sangkhatrap, head of Thailand's Internal Security Operation Command, said heightened security measures would be in effect through March 22. He did not give details of the measures or any specific security threats.

"Certain groups of people have plans to actively instigate violence during this period," he said.

Drive-by shootings and bombings occur almost daily in Thailand's three Muslim-majority provinces — Yala, Narathiwat and Pattani.

Violence has increased since a military-installed government took power in September following a coup that ousted then-Prime Minister Thaksin Shinawatra.

Police, soldiers and Muslims viewed as collaborators with the government, along with Buddhist civilians, are targeted by the insurgents.