Updated

At least 78 people were suffocated or crushed to death after being arrested and packed into police trucks following a riot in southern Thailand over the detentions of Muslims suspected of giving weapons to Islamic separatists, officials said Tuesday. Six others were shot to death during the demonstration.

Islamic leaders accused Thai troops of overreacting to the police station protest in Narathiwat province (search) in Thailand's Muslim-dominated south. They also warned it could trigger a spiraling upswing in violence.

"I am in shock," Abdulraman Abdulsamad, chairman of the Islamic Council of Narathiwat (search), told The Associated Press. "I cannot say what is going to happen, but I believe that hell will break out."

The 78 dead were among some 1,300 people arrested after the riot.

Dr. Pornthip Rojanasunan, a forensics expert for the Justice Ministry, said Tuesday that she and other doctors conducted autopsies on the 78 bodies at an army camp in Pattani province (search) and found that most died from suffocation.

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 began Monday when about 2,000 Muslim youths demonstrated outside the police station in Takbai district (search), demanding the release of six men held on suspicion of stealing state-issued weapons and giving them to Islamic separatists. The crowd threw rocks, overturned a military truck and made several attempts to storm the police station and a nearby government office.

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 360 people have been killed in southern Thailand since January, mostly in small bombings 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 of 84 dead 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.

Prime Minister Thaksin Shinawatra (search) visited the southern region briefly late Monday, where he praised the security forces and vowed tough action against suspected Islamic separatists.

"The protesters had several motives, but the main reason was separatism," Thaksin said, speaking before the announcement of the 78 suffocation deaths. "I cannot allow the separatists to exist on our land."

He added: "We cannot allow these people to harass innocent people and authorities any longer. ... We have no choice but to use force to suppress them."

At the Inkayut military camp where prisoners were being held, people came all day Tuesday to report missing family members who might be among the detained. They were not allowed in the camp but registered at the gate, and several dozen families stayed nearby all day, waiting for news.

Authorities announced a curfew in parts of Narathiwat "because the situation is still volatile," Thaksin said.

Neighboring Malaysia — a Muslim-dominated country — expressed concern over the crackdown.

"Thailand is a close neighbor. Any incident will be watched closely here. We are sad that there has been an accident" leading to deaths, Malaysian Foreign Minister Syed Hamid Albar said. "We want to know exactly what happened."