BANGKOK, Dec 3 — Thai authorities filed fresh legal action today against a pro-democracy protest leader after he criticised a court ruling that kept the prime minister in office.

The kingdom’s constitutional court yesterday ruled Prime Minister Prayut Chan-O-Cha was not guilty of a conflict of interest by living in an army residence after leaving the military.

The ruling angered some 5,000 protesters who took to the streets, and student leader Parit "Penguin” Chiwarak encouraged the crowd to raise their middle fingers at the judges, defying a court warning against "vulgar” criticism.

A court representative filed a contempt case against him at the Technology Crime Suppression Division in Bangkok today, citing his Facebook posts and speeches on stage.

It is the latest legal challenge to the youth-led protest movement that has shaken Thailand since July calling for Prayut’s resignation, constitutional reform and changes to the once-untouchable, ultra-rich monarchy.

Five protest leaders including Penguin have been charged under the kingdom’s strict royal defamation laws, which prohibit any criticism of the king and his family.

And more than 170 other protesters have been charged — nearly 50 for "sedition”, which can carry a seven-year prison sentence. — AFP