By Panarat Thepgumpanat and Chayut Setboonsarng
BANGKOK (Reuters) - Thai Prime Minister Prayuth Chan-ocha threatened on Thursday to use all laws possible against protesters, as demonstrations escalate for his removal and for reforms to curb the powers of King Maha Vajiralongkorn.
Activists voiced concern that this could mean the resumption of prosecutions under some of the world's harshest royal insult laws.
"Prayuth has declared a battle against the people," said rights lawyer and protest leader Arnon Nampa. "For civil servants who have not chosen sides, you need to decide whether to live in the past or to build a future with us."
The protests since July have become the greatest challenge to Thailand's establishment in years and have broken a longstanding taboo by criticising the monarchy, which can carry a jail term of up to 15 years.
Prayuth's announcement came a day after thousands of protesters threw paint at the headquarters of the police in what they said was a response to the use of water cannon and teargas that hurt dozens on Tuesday, the most violent day of protests since July. Some protesters also sprayed anti-monarchy graffiti.
"The situation is not improving," Prayuth said in a statement. "There is a risk of escalation to more violence. If not addressed, it could damage the country and the beloved monarchy.
"The government will intensify its actions and use all laws, all articles, to take action against protesters who broke the law."
He did not specify whether this included Article 112 of the criminal code, which forbids insulting the monarchy. Prayuth said earlier in the year that it was not being used for the moment at the request of the king.
Police have been collecting evidence since July for possible prosecutions for violating the article but had not taken further steps, one police source said.
Outraged by the anti-monarchy graffiti at Wednesday's demonstration, some royalists called for the application of Article 112 in posts on social media.
Dozens of protesters, including many of the most prominent leaders, have been arrested on a variety of charges in recent months, though not for criticising the monarchy.
There were nearly 100 prosecutions for violations of the royal insult laws under the junta that Prayuth led after seizing power in a 2014 coup, but there have been none since 2018, according to data from rights group iLaw.
Protesters accuse Prayuth of engineering an election last year to keep stay on in power as a civilian prime minister. He says the ballot was fair.
A major protest is planned at the Crown Property Bureau on Nov. 25 over the management of the palace fortune, which the king has taken into his personal control. The fund is valued in the tens of billions of dollars.
Protesters said there would be seven more days of demonstrations after that.
(Additional reporting by Chayut Setboonsarng and Petra Mahira; Writing by Matthew Tostevin; Editing by Stephen Coates, Robert Birsel)