WASHINGTON (AFP) - The United States said Tuesday that a Muslim insurgency in southern Thailand was "very worrisome" but did not anticipate any role in helping to resolve the turmoil.

More than 3,300 people have been killed since separatist unrest broke out in January 2004, and militants' tactics have turned increasingly gruesome, with a US rights group reporting that beheadings, live burnings and torture have become a common feature.

"The insurgency in southern Thailand is very worrisome, I know it is very worrisome to the Thai authorities," Scot Marciel, the US envoy to the Association of Southeast Asian Nations (ASEAN), told a forum of the Washington-based Woodrow Wilson International Center for Scholars.

He said the new government of Thai Prime Minister Samak Sundaravej was formulating a strategy to contain the insurgency.

"It's gotten better but it hasn't got dramatically better. So it remains, I think, a very serious problem -- one I know the Thai government takes very seriously," Marciel said.

The southern border states formed an autonomous Malay Muslim sultanate until predominantly Buddhist Thailand annexed it in 1902, provoking decades of tension.

Authorities have made little progress in identifying the militants, who rarely claim responsibility for their attacks.

Marciel said the problem could not be resolved purely by military means, noting that the previous government used security and law enforcement to contain the crisis combined with efforts to win the "hearts and minds" of the people.

But the United States was not likely to get involved.

"We do not anticipate a US role. I don't think that would be productive, I don't think the Thais think it would be productive," he said.

"If there is something useful we could do and are asked, we would certainly consider. At this point, we are just watching it."

Human Rights Watch spoke out Tuesday over the targeting of civilians and brutal killings in Thailand's south, warning that beheadings, live burnings and torture were becoming common.

"Insurgent groups continue to unleash brutality on civilians to demonstrate their power and weaken the credibility of Thai authorities," Brad Adams, Asia director at Human Rights Watch, said in a statement.

On July 4, insurgents beheaded Khan Sangthong, a 55-year-old Buddhist, in nearby Yala province. He was shot, burned and had nails hammered through his hands before being decapitated.

His severed head was placed on a bridge yards from his body.

Human Rights Watch said more than 20 Buddhist Thais have been beheaded by insurgents across the southern border provinces in the last four years.

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