A prominent student activist was indicted Friday in the first royal defamation case brought under Thailand's new monarch, his lawyer said, after the UN urged the kingdom to scrap its lese majeste law.

Jatupat Boonpatararaksa was arrested in December for sharing on Facebook a profile of King Maha Vajiralongkorn written by the BBC's Thai-language service in London.

Criticising the royal family is punishable by up to 15 years in prison per count in Thailand, where the law is broadly-interpreted and aggressively enforced.

Scores of lese majeste cases have been brought against members of the public and activists in recent years, often for comments made online.

Jatupat, better known by his nickname Pai, was indicted by a court in northeastern Khon Kaen province Friday, his lawyer Krisadang Nacharut told AFP.

"He is still in good spirits and will fight," Krisadang said, adding that the activist has also been charged with violating the Computer Crimes Act -- another tough law used to punish online defamation. Jatupat has denied both charges.

While thousands shared the article, Jatupat -- a prominent critic of the country's military junta -- is the only person to have been prosecuted so far.

The 25-year-old law student had already been detained for more than 50 days, after judges rejected multiple requests for his release on bail in closed-door hearings.

The UN this week expressed concern over the secret proceedings and called for Thailand to repeal the lese majeste law.

Jatupat's lese majeste charges are the first to be taken up in court since King Vajiralongkorn ascended to the throne in December following the death of his revered father, whose reign spanned 70 years.

Observers are closely watching whether the new monarch endorses or backs away from the royal defamation law.

The lese majeste law effectively bars public scrutiny of key royal figures, spawning a culture of self-censorship across media, academia and arts.

The profile shared by Jatupat contained details of 64-year-old Vajiralongkorn's personal life that are well-known inside the kingdom but rarely printed by the Thai press.

The new king has spent much of his life abroad and does not enjoy his father's widespread popularity.