They have opened fire on its Buddhist passengers and killing other eight people too on tuesday.
It was told by the police that when the van was slowed down in a curve the insurgent bombed first, then shooted on the drivers face and then opened the side to attack on each of the passenger.
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. All of the passengers were identified as Buddhists and the driver was Muslim.
All the security were pushed on Tuesday on the occassion of anniversary of the founding of the Barisan Revolusi Nasional, or National Revolution Front separatist group. There were alert expecting any violence in the place too.
Violence has increased since a military-installed government took power in September following a coup that ousted then-Prime Minister Thaksin Shinawatra