The police are preparing to charge four key figures behind the political rally outside Government House on Thursday for organising a public gathering in violation of the Disease Control Act and the emergency decree, says the Metropolitan Police Bureau (MPB).
MPB's deputy chief, Pol Maj Gen Piya Tawichai, said authorities have identified four leaders of the UNME of Anarchy group, who will be summoned to acknowledge the charges at Nang Loeng police station on April 25.
The group used its social media channels to get its supporters to gather near Chamaimaruchet Bridge.
Around 50 people showed up, despite repeated police warnings that the gathering was unlawful, he said.
Separately, a member of the We Volunteer (WeVo) group who acted as a security guard for the Ratsadon Group at their past rallies revealed in a Facebook post that he tested positive for Covid-19 on Friday.
Activist Nattapong Kom-jan released a timeline of his movements following his diagnosis, urging those who came into close contact with him to get tested for Covid-19.
Among the events he attended was last Saturday's United Front of Democracy against Dictatorship (UDD) rally at Khok Wua intersection and the Democracy Monument.
Amid concern following the news, UDD chairman Jatuporn Prompan announced via Facebook live that the group and its allies will only go ahead with their planned rally next Saturday if the number of daily new infections continues to decline.
If the Covid-19 situation in Thailand has not improved, the group will move its activities to social media, he said. It is unclear what form such a protest would take.
In his address, Mr Jatuporn called for the release of protest leaders detained in prison for their role in past protests, saying they deserve to be freed on bail.
If something unexpected happens to any of the detained protest leaders who are on a hunger strike, the political situation will worsen, he said.