The announcement dramatically increased the total death toll from the latest eruption of violence in Thailand's Muslim-dominated south to 84. Officials had earlier said that six people were shot to death during clashes Monday at a police station in Narathiwat province.
Dr. Pornthip Rojanasunan, a forensics expert who works for the Justice Ministry, told a news conference Tuesday that she and a team of doctors conducted autopsies on 78 bodies at an army camp in Pattani province and found that most had perished from suffocation.
The dead were among some 1,300 people that military officials said they had arrested Monday following the police station riot.
Maj. Gen. Sinchai Nujsathit, deputy commander of the fourth army, said the victims may have died from suffocation "because we had more than 1,300 people packed into the six-wheel trucks."
He did not say how many trucks were used.
Manit Suthaporn, deputy permanent secretary of the Justice Ministry, said the victims probably suffocated because they were piled on top of each other in the vehicles.
The violence erupted Monday when about 2,000 Muslim youths demonstrated outside the police station in Takbai district, demanding the release of six detained men.
Police and military forces tried to disperse the crowd with gunshots, water cannons and tear gas. Six people were killed and several injured in the melee, army commander Gen. Pisarn Wattanawongkhiri said Tuesday.
More than 400 people have been killed in southern Thailand since January. Most have died in small bomb attacks and drive-by shootings directed at police and government officials. Authorities blame the violence on a renewed Islamic separatist insurgency.
Violence has troubled overwhelmingly Buddhist Thailand's three Muslim-majority provinces for decades, although it has worsened this year. Residents claim they are discriminated against by the central government.
The toll from Monday's violence was the largest from a single incident since April, when police and soldiers responded with overwhelming force to attacks by alleged Islamic militants armed mostly with machetes, killing 107.
Islamic leaders accused Thai troops of overreacting to the police station protest and warned it could trigger an upswing in violence.
"I am in shock," Abdulraman Abdulsamad, the chairman of the Islamic Council of Narathiwat, told The Associated Press on learning of the suffocation deaths. "I cannot say what going to happen, but I believe that hell will break out."
Prime Minister Thaksin Shinawatra visited the region briefly late Monday, where he praised the security forces and vowed tough action against suspected Islamic separatists.
"We cannot allow these people to harass innocent people and authorities any longer ... we have no choice but to use force to suppress them," Thaksin said, speaking before the announcement of the 78 suffocation deaths.
Authorities announced a curfew in parts of Narathiwat after the violence "because the situation is still volatile," Thaksin said.
Investigators, meanwhile, searched for weapons at the rioting site and in a nearby river, where divers were also looking for bodies.
Monday's rioters, who were demanding the release of six men detained on suspicion of stealing state-issued weapons from defense volunteers, hurled rocks, overturned a military truck and made several attempts to storm the police station and a nearby government office.
Neighboring Malaysia — a Muslim-dominated country — expressed concern over Monday's crackdown.
"We are very concerned," Prime Minister Abdullah Ahmad Badawi told reporters. "We hope the government of Thailand will be able to manage this crisis so that it will not spread and inflame further violence."
By Alisa Tang