Thailand has asked social networking website Facebook to delete more than 10,000 pages of content containing images or text which it claims are "offencive" to the monarchy, a minister said on Thursday.

The news comes a day after a Thai court jailed a man for 20 years for sending four text messages deemed insulting to the monarchy, alarming critics who say the kingdom's strict lese-majeste laws hamper free speech.

"We have informed Facebook and sought their assistance in deleting content which is offencive to our monarchy," the country's information minister Anudith Nakornthap told AFP.

"There are more than 10,000 URLs which seem to insult the monarchy," he said, adding that people should not click "Like" or comment on "offencive" posts as this would be considered indirect dissemination of the material.

Under Thai law, anyone convicted of insulting the king, queen, heir or regent can face a prison sentence of up to 15 years for each offence. Even repeating details of an alleged offence is illegal.

In the last few weeks, a number of pro-monarchy Facebook pages have appeared, including one encouraging users to flag content which could be in violation of lese-majeste laws.

The royal family is a very sensitive subject in Thailand and 83-year-old King Bhumibol Adulyadej, the world's longest-reigning monarch, is revered as a demi-god by many Thais.

Academics have noted a sharp increase in new royal insult cases in recent years and rights groups have expressed concern that the law was used to suppress freedom of expression under the last pro-establishment government.

Observers say the new government of Prime Minister Yingluck Shinawatra, who came to power in August, has yet to improve the situation.

Last month a Thai-born US citizen, Joe Wichai Commart Gordon, pleaded guilty to insulting the monarchy, in a case that prompted the UN special rapporteur on freedom of expression to urge Thailand to amend the lese-majeste laws.

A prominent Thai website editor is also facing up to 20 years in jail for allegedly failing to remove other people's online remarks deemed critical of the monarchy from her website quickly enough in 2008.