Thailand's prime minister has admitted that the army made mistakes dealing with an anti-government demonstration that left dozens of people dead.

At least 78 people were suffocated while being transported on army trucks after they were arrested. The demonstrations, which took place Monday in the southern part of the country, were protesting the arrest of six Muslim men.

Prime Minister Thaksin Shinawatra apologized in the county's senate as relatives flooded an army camp to claim the bodies.

"There were some mistakes," said Thaksin, who said the army didn't have enough trucks to transport those arrested. Soldiers had to "pile them up on top of each other, and they died," he said.

"We are sorry for that, sorry they met an untimely death," Thaksin told the Thai senate.

A senior Thai security official said the military used four trucks to move more than 1,300 people, who spent about six hours packed in the vehicles.

Analysts say there's a growing Muslim separatist movement in Thailand's three southernmost provinces.

Thaksin blamed the growing unrest on separatists he says are linked to Islamic leaders distorting the Qur'an to promote violence.