BANGKOK - THAILAND'S best-known social critic Sulak Sivaraksa was arrested in Bangkok for insulting the kingdom's monarchy, police said on Friday.

British-educated Sulak, 76, was arrested in connection with a speech he delivered at the northeastern Khon Kaen university in December last year.

The criminal charge of lese-majeste carries a maximum 15 years imprisonment.

'He was arrested at his residence early on Thursday evening in accordance with a court-approved arrest warrant issued on September 22. He was brought to Khon Kaen immediately', said a Bangkok police spokesman, who refused to be named.

It is not the first time Mr Sulak has been arrested on the charge. In 1984 international protests led to his release after he was taken into custody by authorities.

But he was charged in September 1991 after a lecture he gave at Bangkok's Thammasat University - causing him to flee abroad until he could overturn the charge in 1995.

In an interview with local media last month Mr Sulak said he had been arrested a third time on the same charge but gave no details.

Mr Sulak is well-known abroad as a prominent Buddhist working for human rights, and is a vocal critic of deposed Thai premier Thakin Shinawatra.

His arrest comes as street protests by opponents of the former prime minister and current government enter their seventh month, and the week before the funeral of the king's sister, who died in January.

Thailand's laws make it illegal to insult the king, who turns 81 on December 5 and who many Thais believe is semi-divine.

In September a Thai court ordered hundreds of websites to be shut down for carrying content disrespectful to the royal family.

That followed the arrest of an Australian author in August for criticising the king's son.

The video-sharing service YouTube was also banned for five months last year over videos mocking King Bhumibol Adulyadej until it was agreed filters would be put in place to censor the content. -- AFP