Hundreds marched in Bangkok and lit ceremonial fires in front of a courthouse on Saturday to protest Thailand's draconian royal defamation law and the jailing of several prominent pro-democracy activists.
The protesters are part of a youth-led movement that kicked off last July calling for an overhaul to Premier Prayut Chan-O-Cha's government and a scrapping of the country's military-scripted constitution.
They are also demanding the abolition of a lese majeste law which shields the kingdom's ultra-powerful King Maha Vajiralongkorn and the royal family from defamation, and carries penalties of up to 15 years per charge.
The law has been broadly interpreted to cover anything perceived as negative towards the royals, effectively muzzling critics -- which is why the movement's calls for reforms have sent a lightning bolt through Thai society.
As protesters marched to Bangkok's criminal court, they chanted "Prayut, Get Out!" and "Abolish 112" -- the penal code section of the lese majeste law.
"The younger generation have the same objectives as me," said Kanokwan, 51.
"I don't fear violence and I want a new government, a new constitution and monarchy reform."
When they arrived at the court, some protesters piled up garbage and set it on fire beneath a portrait of the king, as others held up posters depicting prominent activists currently behind bars for lese majeste.
Protesters chanted the names of human rights lawyer Anon Numpa and student leader Parit Chiwarak -- better known as Penguin.
They also called for the release of Anchan, a former civil servant who was jailed in January for more than 43 years for insulting the monarchy -- the harshest sentence ever handed out for lese majeste in Thailand.
Around a dozen activists were arrested by the end of the night, an AFP journalist on the ground said.
The protest at the criminal court was one of three anti-government rallies organised across Bangkok Saturday.
The pro-democracy movement had slowed in recent months, but the jailing of several prominent activists in February have galvanised supporters to return to the streets.
They clashed last Sunday with police, who deployed rubber bullets, water cannon and tear gas against them -- the first use of force, albeit non-lethal, in months.
More than 20 protesters were arrested, while authorities confirmed the death of one police officer 'during the operation'.
"Protesters look like they are trying to level up... intensity and violence," National Police chief Suwat Chaengyodsuk told reporters Friday, warning that authorities will be prepared to "take care of the situation".
Some 4,800 officers were deployed across the Thai capital on Saturday.
Earlier in the day, a small group of royalist supporters protested downtown against the pro-democracy movement, shouting "We live and die as a royalist".
"We want to show our feelings that we love our monarchy and the king," said a business owner nicknamed Tew, 58.
"Our monarchy does not need to reform."