BANGKOK, Thailand -- Thai security forces allegedly burned, buried, sodomized and stuck needles into victims, and abandoned people in the sea to die, according to survivors and human rights groups, but the prime minister and military denied systematic abuse.

Alleged cases involve three very different minority groups, in three geographical regions, including:

-- Boat refugees in the Andaman Sea who are Muslim ethnic Rohingyas from Bangladesh and Burma.

-- Suspected Islamist guerrillas and civilian sympathizers who are Malay-Thais living in Thailand's violent south.

-- Illegal overland immigrants from Laos, who crossed the Mekong River into Thailand's north and are ethnic Hmong animists, Buddhists and Christians hoping Washington will save them.

Thailand's new Prime Minister, Abhisit Vejjajiva, denied Bangkok had a policy of torturing detainees, and promised to investigate.

Thai military officials echoed his denial, and said they too would determine the veracity of the allegations.

The newest alleged atrocities involve desperate Rohingyas, who paid hundreds of dollars to human traffickers, climbed into fishing boats, and journeyed across the Bay of Bengal into the Andaman Sea.

Destinations included Southeast Asia's relatively prosperous Thailand, Malaysia, and Indonesia.

The Rohingyas expected to join other undocumented workers who are exploited by construction crews, the fishing industry, and sweat shops.

Some Thai officials said the boats brought young male Muslims, who could be foreign Islamist guerrillas joining the bloody separatist struggle in southern Thailand.

"We were tied up and put into a boat without an engine," Zaw Min told the Bangkok Post, describing how hundreds of Rohingyas were allegedly treated by Thai security forces after landing on the small island of Koh Sai Daeng, off Ranong province, on December 18.

"We were then towed into the high seas by a motor boat, and set adrift," he said after India's coast guard rescued them, though an estimated 300 others allegedly perished at sea.

"Thai authorities obviously wanted us to die on the boat."

Thai officials insisted they gave the Rohingyas food, repaired their boats, and convinced them to travel on, denying a Bangkok-based Arakan Project advocacy report which said four were deliberately killed.

"The locals asked the Rohingyas where they wanted to go, because they could not stay here. Some mentioned Malaysia and others chose Indonesia," the Internal Security Operations Command's Col. Manas Kongpan told Parliament on Wednesday (January 21).

"As for the report that some were starving, that might be because they were lost, or the winds changed," Col. Manas said.

On Thursday (January 22), the United Nations High Commissioner for Refugees (UNHCR) and the Thai government were unable to agree on an international investigation into the allegations.

About 4,800 Rohingyas were arrested for illegally entering Thailand during the past year.

Meanwhile, Thai citizens said they were tortured in Thailand's south, including at Ingkharayuthboriharn Army Camp in Pattani province.

London-based Amnesty International's 37-page January report, about suspected Islamist guerrillas and sympathizers, "documents people being brutally beaten, burned with candles, buried up to their necks in the ground, subjected to electric shocks, having needles stuck into various parts of their bodies, sodomized, and exposed to intense heat or cold," the human rights group said.

"Survivors of torture told Amnesty that the most common torture techniques they faced were beatings, being kicked or stomped on, and having plastic bags placed over their heads until they nearly suffocated. Amnesty International established that at least four people have died as a result of torture," it said.

"The research in the report focused on incidents between March 2007 and May 2008," and indicated that "Thai authorities need to pay special attention to ending abusive practices at the base," Amnesty said.

Torture is "not government policy, and it was not carried out systematically," Prime Minister Abhisit said on January 14, responding to Amnesty International.

"The government does not support use of extra-judicial power."

The regional insurgency, which killed 3,200 people on all sides since 2004, is fueled by Islamist demands for independence or autonomy, and Muslims suffering under Buddhist-majority Thailand's southern martial law.

"Violent attacks have become more frequent [during December], as we have taken harsher action to suppress insurgent groups," said the south's Fourth Army commander, Lt.-Gen. Pichet Wisaijorn.

Islamist assaults included gory beheadings, assassinations, bombings, and arson against military and civilian targets.

Elsewhere, in northeast Thailand, allegations of Thai brutality were made by Hmong refugees, including elderly mercenaries previously paid by the U.S. Central Intelligence Agency during their failed war against communism in Laos, which ended in 1975.

Young Hmong were described as the mercenaries' descendents, victimized by the current Lao regime because of their ancestors' past CIA collaboration.

Laos denied persecuting the Hmong, and said the men, women and children were murderous bandits in the jungles, or economic migrants illegally entering Thailand for a better life.

They were tricked into believing Washington would greet them with open arms, Laos said.

"President Obama, remember your promise to the Hmong," said Joe Davy, a Chicago activist for the Hmong.

"You have pledged that, 'The U.S. must be clear in calling for all parties to respect international law, and ensure that displaced Hmong are not placed in harm's way'," Mr. Davy said on Tuesday (January 20) quoting campaign oration.

"There is a group of 158 UNHCR-recognized refugees currently in urgent need, who are being held hostage under torturous conditions at Nong Khai immigration jail, Thailand," he said, describing Hmong families who illegally entered from Laos two years ago.

***** Richard S Ehrlich is a Bangkok-based journalist who has reported news from Asia since 1978. He is co-author of "Hello My Big Big Honey!", a non-fiction book of investigative journalism, and his web page is http://www.geocities.com/asia_correspondent