Unknown assailants staged attacks in Yala province on Sunday

They arrived as Prime Minister Thaksin Shinawatra announced that he believed the attacks were religiously motivated.

The BBC's Tony Cheng says the statement marks a significant shift from Mr Thaksin's previous positions on who was responsible for the violence.

Mr Thaksin last week blamed drug-crazed teenagers and armed bandits.

The troops' arrival follows another attack on the authorities on Sunday night. In Yala province, three rounds of M-79 rockets were fired on a security post, and a government office was set on fire, police said.

The government has so far given conflicting views on who is behind the violence - Mr Thaksin has blamed criminal gangs, while Defence Minister Chettha Thanajaro has said they were mounted by Muslim militants.

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On Monday Mr Thaksin seemed to come into line with that opinion.

"From our investigation," he said, "it is clear that there are people perverting religion."

He went on to suggest that those involved in the attacks had been manipulated into doing so for religious reasons, and that they had been paid.

A BBC correspondent in Bangkok, Tony Cheng, says the government has been very keen to play down the role of religion in the violence that has gripped the majority Muslim southern provinces since January.

He says it fears further alienating the local population, who feel politically and economically isolated from the rest of the country.

The fresh contingent of troops arrives amid concerns among human rights groups and locals that excessive force was used in response to the violence.

More than 100 youths were killed by security forces on Wednesday, after they carried out raids on police and army posts in three southern provinces.

Our correspondent says many of the new troops who arrived on Monday have had experience in a multilateral peacekeeping force in East Timor, and are hoping those experiences will help them win the hearts and minds of the local population.

Despite the attacks on Sunday night, in which one security official was wounded, our correspondent says that some semblance of calm has returned.

But he says that, beneath the surface, tensions are still running very high.

Mr Thaksin will visit the south this week, according to local news reports.

"I will go, even though the situation is still volatile," he told reporters. "I want to talk to the parents of those boys who have been misled because they need somebody to advise them. Some families do not even know what their children have been doing," he said.