Thai police used water cannon and rubber bullets outside Bangkok's Grand Palace Saturday, after demonstrators broke through a barricade of shipping containers to demand reforms to the kingdom's unassailable monarchy.
It was the latest night of unrest since Thailand's pro-democracy movement kicked off in July, calling for an overhaul of Premier Prayut Chan-O-Cha's administration and a rewrite of a military-scripted constitution.
But their most controversial demands have been for reforms to the monarchy, including the abolition of draconian royal defamation laws.
A wall of cargo containers, two containers tall, had been erected in Sanam Luang, a historic field in front of the palace, to keep protesters away but, just an hour into the rally, they used ropes to yank some of the top-row boxes down, allowing a small opening.
"You're breaking the law!" said the police over an announcer as protesters used ropes to pull the lower containers out of place.
Once protesters were able to get through, they threw Molotov cocktails at dozens of police who stood by with water cannon trucks about 100 metres (300 feet) away, using the jets to prevent protesters from coming closer.
"Release our friends!" protesters shouted, referring to prominent leaders who have been detained since earlier this year.
Police chased demonstrators away from the area, firing rubber bullets continuously directly at them, according to AFP reporters on the ground.
By 8.30 pm (1330 GMT), most protesters had dispersed, with only hard-core activists still at the scene.
- 'We need to come out' -
Before the clash, protester Am-Nawat Liangwattana said the use of shipping containers as barricades meant authorities were getting serious about "limiting our freedom of speech".
Protesters had planned to read aloud passages from "The Institution of Monarchy in Thailand's Society", a book authored by now-detained prominent protest leader Anon Numpa.
Earlier in the day, police had raided Thai publishing house Same Sky Books and confiscated some 100 copies of Anon's book.
"The authorities might be afraid of the content... But the more they confine us, the more we need to come out," Am-Nawat said.
The reading did not happen, because of the police crackdown.
Of the books, Police Major Trirong Prasopmongkol told AFP the force would "have experts examine the content to see whether it is illegal".
"This raid is related to the protest today because protesters said on social media that they will distribute these books," he said.
Same Sky Books later said on its Facebook page that while it had copies of Anon's book, "we were not the ones who printed them".
Since the movement kicked off, more than 60 people have been charged under Thailand's royal defamation laws, and a handful of the most prominent leaders have been detained.
The laws shield the ultra-powerful King Maha Vajiralongkorn and his family from defamation, but rights groups say their broad use means anything perceived as criticism can land a person in jail for up to 15 years per charge.
During Saturday's clashes, the monarch was visiting the historic city of Ayutthaya -- about 80 kilometres from the capital -- with the queen and his royal consort, according to the nightly royal news.