Eleven troops were killed late Thursday when their truck was bombed and ambushed by suspected separatist rebels in Yala, one of Thailand's Muslim-majority provinces bordering Malaysia.

A twelfth soldier died early Friday morning, hospital sources said. The attack came with security forces already stretched by a national clampdown after ex-prime minister Thaksin Shinawatra and his party were barred from elections.

"The militants have stepped up attacks in order to increase pressure on authorities," army spokesman Acra Tiproch told AFP, adding that one more death had been added to the overnight toll.

"This was the biggest single attack yet," he said.

He said that the rebels hoped to provoke a heavy-handed reaction from security forces, who could then be blamed for committing atrocities against residents in the south.

Despite a series of peace-building measures, Thailand's military-backed government is under fire for failing to quell the insurgency which has claimed some 2,200 lives since erupting January 2004 and only appears to be worsening.

Prime Minister Surayud Chulanont, who was in crisis talks on the south with army chief General Sonthi Boonyaratglin Friday morning, promised not to retaliate.

"We must be patient ... we have to be firm on the rule of law. We will not do anything to cause more problems and injustice," he said, but added that it would be impossible to gain the support of many militant sympathisers.

An estimated 2,000 students and villagers protested in a Pattani province mosque for the second day Friday to demand the end of a state of emergency and the immediate withdrawal of troops.

Provincial authorities say the demonstration was organised by militants.

Pattani's governor Panu Uthairat has repeatedly tried to calm the crowds, urging them to go home while armed soldiers and police blocked the roads around the mosque.

As the unrest increases, many districts in Yala, Narathiwat and Pattani provinces have become virtual no-go zones for government troops.

Both soldiers and civilians die each day in shootings and bombings, while the region has also been plagued by frequent arson attacks.

"The situation in the south is getting worse day by day. The militants are stepping up violence to show to the government that they cannot help people in the south," said Srawut Aree, a senior researcher at Chulalongkorn University's Muslim Studies Centre.

Others say Thursday's attack showed that the militants were becoming more sophisticated and confident in confronting better-equipped government troops.

"The latest attack showed that militants are increasingly capable of attacking armed security forces," said Panitan Wattanayagorn, a security expert and political science professor at Chulalongkorn University.

"The militants are becoming more confident in launching big attacks against the military," he added.

The attack against the soldiers capped one of the bloodiest days in the recent history of the insurgency.

Earlier Thursday five young men were gunned down in a mosque in the Saba Yoi district of Songkhla province, which borders Yala and has also seen a spike in separatist violence.

A sixth victim from the mosque attack died Friday, police said.

Elsewhere in the south, two people, including another soldier, were shot and killed, while nine troops were wounded in a series of bomb blasts.