Dr Pornthip Rojanasunan, a well-known pathologist in Thailand, told a news conference that she and a team of doctors conducted autopsies on 78 bodies at an army camp in Pattani province and found that most of the dead had perished from suffocation.
"Seventy-eight people died from suffocation. We found no wounds on their bodies," senior justice ministry official Manit Sutaporn told a news conference in the southern town of Pattani.
The dead were among some 1300 people arrested on Monday following a riot in Thailand's Muslim-dominated southern provinces, which have been struck by unrest this year.
The region was rocked by sporadic violence overnight despite a curfew imposed after clashes on Monday between security forces and demonstrators left six dead and dozens injured.
Police had said the situation was under control on Tuesday morning after the biggest outbreak of violence between the authorities and disaffected Muslims since a day-long clash in April left 108 dead.
Cause of violence
The violence erupted late on Monday after a six-hour demonstration held by about 2000 protesters outside a police station in Narathiwat province's Takbai district to call for the release of six detained security volunteers accused of giving their weapons to insurgents.
Thai police and military forces say they tried to disperse the crowd with gunshots, water cannons and tear gas canisters.
Witnesses say the police fired live rounds into the air and at the crowd.
Commander General Sirichai Thanyasiri, who heads a new task force to improve security in the southern provinces, said:
"The leaders and core members who created the riot will be put on trial and the unwitting followers will be released soon, but I cannot say exactly when."
Rights groups have accused
Thailand of heavy-handedness
Abd al-Rahman Abd al-Samad, chairman of the Islamic Council of Narathiwat province, said the security forces should have acted with greater restraint.
"I think the armed forces overreacted by using force to disperse the protesters," he said.
"If they were more patient and used a softer approach, the incident would not have ended up with lost lives and arrests.
"Some were demonstrators, some were people who went to watch what was going on and there were innocent people affected by the crackdown."
Rights activists have accused the authorities of heavy-handed tactics in the south, including the storming of a 16th century mosque that left 32 people dead in an April massacre where the total death toll was 108.
Southern Thai Muslims remain anguished over the massacre at the historic mosque in the province of Pattani, he said.
Muslims say the memory of the
mosque massacre is still fresh
"The memory is still fresh, and with the latest killings, I am afraid that there will be more violence and revenge from Muslim people," Abd al-Samad said.
At the time, Thailand's national human rights commissioner, Wasant Panich, reportedly said he had documented many accounts from witnesses that police had often killed suspects who were incapable of fighting back.
Thai Prime Minister Thaksin Shinawatra then defended the actions of his security forces and refused to heed a UN call for a probe into the matter.
The premier, who rushed to the scene of this week's violence before returning to Bangkok late on Monday, insisted the crackdown was justified.
"We cannot allow these people to harass innocent people and authorities any longer," Thaksin said.
"We cannot tolerate these bad things any longer. The bad-intentioned people instigate the youths to create violence and chaos, so we have no choice but to use force to suppress them," he added.
Thai Muslims say they have legitimate frustrations, due to economic deprivation and the denial of land rights, freedom of religion and language, as well as the right to run their own schools and to live a lifestyle of their choice.
Muslim leaders had also issued statements saying the way to peace is to address their long-standing grievances.
They say that governments have found it more convenient to join the US-led western chorus and simply branded them as "militants or terrorists" and by so doing, giving themselves the licence to harass and violate the basic human rights of innocent people.
Human Rights Watch (HRW) and other rights groups have consistently been reporting cases of torture, kidnapping and disproportionate force by Thai security personnel.
Malaysian Foreign Minister Albar
says his country is concerned
Following yesterday's violence Malaysia expressed concern over the latest clash in its northern neighbour.
"The flare up in southern Thailand is a matter of concern to us," Foreign Minister Sayyid Hamid Albar said on Tuesday.
"Thailand is a close neighbour. Any incidents will be watched closely here."
He added that Kuala Lumpur was working closely with Bangkok to develop the troubled south so that economic prosperity would bring peace to the region.
Shinawatra hosted talks with Malaysian Prime Minister Abdullah Ahmad Badawi at the resort island of Phuket earlier this month to flesh out development plans for the three southernmost Thai provinces.
"We are sad there has been an incident. We will wait and see what had happened," Syed Hamid said.
Police Major General Kamon Bhotiyop, commander of police in Narathiwat, said on Tuesday that the police and army had set up security checkpoints and the situation had calmed.