The Department of Corrections yesterday transferred 31 inmates suspected of leading a riot and setting fire at Krabi prison to the maximum-security Khao Bin prison in Ratchaburi.
Ayuth Sintoppant, director-general of the department, said an inquiry panel will be set up to look into the cause of the riot.
He said officials will look into whether prisoners were angry over a Covid-19 outbreak at the prison or they were attempting to escape.
"The suspected ringleaders will face further questioning while police consider legal action against them over the destruction of prison property," Mr Ayuth said.
An inspection of the prison was carried out in the aftermath of the riot, he said, adding that a sleeping hall, a library and documents were gutted by the fire.
A kitchen was also ransacked with knives taken and thought to have been used in the riot, Mr Ayuth added.
"Authorities found three barrels of fuel and a number of knives, hammers and sharp metal rods which we think were used in the rioting," he said.
He said the department has isolated and quarantined infected inmates outside the prison to prevent Covid-19 infections.
More than 500,000 inmates nationwide have been fully vaccinated, Mr Ayuth said.
The damaged prison buildings will be repaired and restored, he said, adding there is a long-term plan to move the prison to a location outside downtown Krabi in the future.
Of more than the 2,000 inmates at the prison, 300 had Covid-19.
After the infected were screened and sent to hospitals, another 1,700 were transferred on Thursday to other facilities due to the extent of the damage the riot caused.
Another 620 inmates were also transferred to Songkhla prison yesterday.
Pol Lt Gen Sarawuth Karnpanich, assistant chief of the national police, said the Royal Thai Police has attached importance to the case.
It had instructed investigators under the 8th Provincial Police Region to determine the cause.
Police said the prisoners were believed to have been making an escape attempt due to anger over the response to a Covid-19 outbreak at the prison complex.
About 300 male prisoners were involved in Thursday's riot, including the suspected ringleaders, police said.