"Security said authorities are concerned that young militants will regroup and cause more disturbances," said Lt-General Chumpol Manmai, head of the National Intelligence Agency.

Although some 107 Muslim teens were killed yesterday in a spate of clashes in Yala, Pattani and Songkhla, their surviving cohorts might seek revenge rather than learn a lesson, Chumpol said.

The clashes with security forces are suspected to have been organised by a separatist group known as Sarigat, a splinter of the Barisan Revolusi Nasional (BRN). Sarigat leaders have recruited Muslim teens in the three southernmost provinces and arranged for combat training in remote jungle areas near the border with Malaysia.

Chumpol said the next seven days were crucial for the young militants to mount attacks. He warned that some 150 militants were involved in yesterday's clashes, but many hundreds more remain at large.

Security authorities in the South continue to be on high alert. Army commander-in-chief General Chaisit Shinawatra said the military was closely monitoring the situation at Pattani's Tung Yang Daeng district, where Muslim teens were congregating in unusually large numbers.

Commenting on the worst violence yet in the South, Prime Minister Thaksin Shinawatra said the situation was under control.

"The clashes lasted several hours because certain perpetrators stole M-16 rifles and M-79 grenades before fleeing to a deserted mosque. It was a lengthy process to smoke them out," he said, referring to the bloody raid on Krue Se Mosque in Pattani.

Thaksin pledged to observe the rule of law in bringing culprits to justice. "Investigators will try to identify perpetrators and their masterminds. Some perpetrators might have fled to Malaysia but the masterminds are likely to remain in the country," he said.

The government is on the right track in trying to unmask the masterminds, he said, voicing regret that the violence had led to Thais killing Thais.