Thai police on Sunday fired water cannon on pro-democracy protesters who were trying to march to the royal palace to deliver demands for reform to the unassailable monarchy.
Student-led rallies have rocked the kingdom since July, with protesters calling for the removal of Premier Prayut Chan-O-Cha -- a former army chief who came into power through a 2014 coup -- and a rewrite to the military-scripted constitution.
The boldest in the leaderless movement have also demanded reforms to the monarchy -- a once-taboo issue -- sending shockwaves through Thailand's arch-royalist establishment.
On Sunday, some 5,000 protesters attempted to march from Bangkok's historic Democracy Monument to the Grand Palace to deliver letters to King Maha Vajiralongkorn, as the police warned them to stop.
As the marchers got closer, police fired water cannon at them. The protesters reacted angrily, shouting: "Why did you use the water cannons against us?"
Authorities had warned earlier in the day that protesters were banned from breaching a 150-metre radius around the palace, and some 9,000 officials were deployed.
Sunday's confrontation was the second time police used water cannon against protesters.
Last month, a peaceful rally in downtown Bangkok saw protesters blasted with chemical-laced water as police bore down -- images that shocked many in Thailand.
Before the march to the Grand Palace on Sunday, the rally at the Democracy Monument was peaceful with protesters chanting "Prayut, get out" and holding up a three-finger salute -- a symbol of the movement.
They also threw flowers into a makeshift cardboard coffin carrying a life-sized mannequin with Prayut's face. Some scrawled messages on it, including "go to hell".
Earlier Sunday, prominent pro-democracy figures called on the king to open dialogue with the protesters.
"We hope you will change your behaviour once and for all and become a King of all people," wrote lawyer Anon Numpa, one of the most recognisable faces in the movement.
"I hope Your Majesty will open your mind and reach out to dialogue with us to solve the crises together."
The unprecedented demands to Thailand's ultra-wealthy monarch have infuriated pro-royalist groups, and they have retaliated with counter-rallies.
On Sunday, a smaller group of the king's supporters came out to the Democracy Monument holding portraits of King Vajiralongkorn, but they left after they were outnumbered by the protesters.