Thirty-three people were confirmed injured during the pro-democracy rally outside the 1st Infantry Regiment barracks in Bangkok on Sunday night, and 22 protesters were detained by police.
Sunday night 's rally, organised by Restart Democracy (Redem) on Vibhavadi-Rangsit Road, was called off shortly after midnight. Redem is the lastest recarnation of the Free Youth group.
The Erawan Medical Centre on Monday reported that 23 police and 10 protesters were treated for injuries received during the clashes.
One police officer on duty died of a heart attack. He was Pol Capt Wiwat Sinprasert, of Thammasala police station, who had heart disease.
Pol Maj Gen Piya Tawichai, the Metropolitan Police Bureau deputy chief, said 22 demonstrators were arrested and were being detained at the Region 1 office of the Border Patrol Police Bureau in Khlong Luang district of Pathum Thani.
Charges to be pressed against them included violation of the emergency decree on Covid-19 prevention, and damaging public property, he said.
Police fired rubber bullets, water cannon and tear gas at the protesters as they pushed through a barrier of empty shipping containers and tried to move closer to the barracks, where Prime Minister Prayut Chan-o-cha lives in an army welfare house.
Police have been criticised for again using violent measures against the protesters.
Pol Maj Gen Piya on Sunday night defended their actions, saying the protest had become violent and government property was being vandalised.
Gen Prayut offered condolences on the death of the police officer, in a statement issued from Government House, and called for police on duty to show patience and for protesters to respect the law.
Police used tear gas, water cannon and rubber bullets against protesters outside the 1st Infantry Regiment on Sunday. (Reuters video)
