Nine protesters were arrested for attacking a police station where a teenager was being held for allegedly breaking Thailand's notorious royal defamation law that protects its king.

Dozens of political activists gathered outside the Samran Rat Police Station in Bangkok on May 10 slamming the detention of Thanalop 'Yok' Phalanchai, 15, who was arrested last March for allegedly violating the country's infamous lese majeste edict. The law criminalises any criticism of the monarch - who is best known for throwing topless birthday parties for his pet dog, walking around in crop tops and keeping a harem of 'sex soldiers' in a German hotel.

Upon learning that police were preparing a new charge against the teenager, they trooped to the station demanding to speak to those in charge.

However, the protest soon turned violent, with the group shattering glass doors and vandalising vehicles and the building itself with red paint. Riot police were dispatched to control the crowd.

Nine people were arrested and held at three different police stations.

Police Colonel Tossaphol Ampaipipatkul, the superintendent of Samran Rat police station, said: 'The incident resulted in a shattered glass door, two police cars damaged by spray, and paint on the walls and floor.

'All nine protesters have been charged with offences including damaging government property, resisting or obstructing authorities, and trespassing at night.

'A request for a warrant for their detention will be made on the afternoon of May 11.'

Section 112 of Thailand's Criminal Code, also known as the lese majeste law, says that 'whoever defames, insults or threatens the King, the Queen, the Heir-apparent or the Regent, shall be punished with imprisonment of three to fifteen years.'

Thailand is said to have the 'world's harshest lese majeste law' with up to 15 years imprisonment for each count.

Critics said broad interpretations of what constitutes an insult to monarchy allow authorities to wield the law against government opponents.

Offenders face lengthy jail terms, with a number of people being exiled or mysteriously disappearing.