The Corrections Department has reported 1,243 new infections and three deaths among inmates, raising the total number of prison cases to 17,138.
Department deputy director-general Weerakit Hanpariphan said all infected inmates were being treated.
He said the first fatality was a 62-year-old man from Chiang Mai Central Prison, who was admitted to Nakornping Hospital on May 11 suffering from exhaustion and died on Tuesday afternoon.
The second inmate was a 64-year-old man at Thon Buri Remand Prison, who was admitted to the Medical Correctional Institution on May 15 with symptoms of exhaustion and low blood oxygen.
He died in the early hours of yesterday.
The third death was a 47-year-old man from Bangkok Remand Prison, who was admitted to the Corrections Hospital on May 10 with a high fever and was placed on a ventilator.
He died at 6.30am yesterday.
Songkhla Prison reported one new case yesterday and a total of 14 prisons had reported infections among prisoners, Mr Weerakit said.
Last week, Chiang Mai Central Prison reported the highest number of Covid-19 cases at 3,929.
Covid-19 infections in prisons were first reported after Panusaya "Rung" Sithijirawattanakul, who was released earlier this month on bail after being held in pre-trial detention, said on her Twitter account after being released that she was being treated in hospital for Covid-19.
Deputy government spokeswoman Rachada Dhnadirek said after the weekly cabinet meeting on Tuesday that it had approved a budget to provide the same health coverage for stateless and foreign prisoners as Thai inmates under the national health security system.
Hospitals where this group of prisoners were admitted had to pay for their treatment, Ms Rachada said.
