City deputy police chief Pol Maj Gen Piya Tavichai said charges would be brought against 11 rally leaders who addressed the demonstrators. Police had already identified 10 of them.
Others would include people using loudspeakers, rally guards and some demonstrators, he said.
People who held up banners with messages insulting the monarchy, and any media that broadcast the illegal messages from the rally with the intention of breaking the law would also be prosecuted, Pol Maj Gen Piya said.
“Teams of police recorded pictures and voices and people will be summoned to acknowledge charges,” he said.
Sonthiya Sawasdee, adviser to the House committee on law, justice and human rights, yesterday (Mar 25) asked police to take action against rally speakers who spoke offensively about the royal institution, and against a satellite TV station that broadcast rally speeches live, without screening the content.
Thousands of demonstrators packed Ratchaprasong intersection on Wednesday evening and into the night, demanding monarchy reforms, an end to the lese majeste law and the release of detained rally leaders being prosecuted for lese majeste and other offences.
Panusaya “Rung” Sithijirawattanakul, a key leader of the protesting Ratsadon group who is being detained at the Central Women’s Correctional Institution, has urged more supporters of the group to come out onto the streets to keep the fight going.
Her message was posted on Wednesday on her Facebook account by her elder sister on her behalf, according to the post.
Ms Panusaya admitted the number of people taking part in the group’s rallies has fallen considerably when compared to last year’s protests.
“The situation now isn’t good at all as we have been put in jail. More of our friends might be detained in prison if they are denied bail,” she said in the Facebook post.
“If everyone isn’t coming out on the streets no matter whether it is fear or complacency that deters you, it could be someone close to you who will walk into prison [as a detained suspect] next time,” she said.
“Democracy will have to continue now and forever, although the people [protesters] may be gone [during this fight]. If you miss us and want us to walk free from prison and don’t want anyone else to come in again, ask your parents and families to join hands and fight for us,” she said.
Prime Minister Prayut Chan-o-cha, meanwhile, called for peace and national unity.