BANGKOK : Thai authorities have threatened to shut down 29 websites over content deemed offensive to the nation's revered king, warning that owners of the portals could face prosecution.

The latest threat comes after Thailand’s 5 month ban of the video-sharing service YouTube last year, over videos that mocked Thai King Bhumibol Adulyadej.

The ban was lifted after YouTube, owned by Internet giant Google, agreed to filter videos related to the king from appearing to users in Thailand.

Thailand's Interior Minister, Chalerm Yoobumrung, said he would be closely monitoring the websites in question and would discuss the matter in a meeting with police.

"We will exercise whatever law we need to, because it's threatening national security and the interior ministry cannot ignore it," he told reporters.

Many Thais believe the King is semi-divine and Internet content deemed overtly critical of him has been under close scrutiny since former Prime Minister Thaksin Shinawatra was toppled in a coup by army generals in 2006.

Thai Special Branch police confirmed that they had more than 20 websites under investigation for insulting the monarchy, including the pro-Thaksin site hi-thaksin.net.

Last year's YouTube controversy centred on a clip posted by an anonymous user showing digitally-altered images of the revered 80-year-old King next to a photograph of feet.

Thais believe feet are the lowest and dirtiest part of the body, and placing them next to someone's head is seen as a massive insult.

Other video clips and webpages covering controversial Thai politics and the monarchy have since been banned.

Lieutenant General Rapipat Palawong, commander of Special Branch Police, said that any website suspected of allowing messages to be posted which insulted the monarchy, whether hosted in Thailand or abroad, would be liable for prosecution.

"We have coordinated with our legal department and Interpol on how to prosecute these perpetrators," Rapipat said, explaining that some of the sites had been found to be registered overseas.

- AFP/cl