Thais should "socially sanction" those who defame the monarchy following King Bhumibol Adulyadej's death, the junta's justice minister has said, amid fresh videos of mob justice against people accused of insulting the institution.

The death of the world's longest-reigning monarch on Thursday has left the nation bereft of its key pillar of unity and seen remarkable mass outpourings of grief from black-clad Thais.

But it has also fired up small but vocal ultra-monarchist forces, including mobs and online crusaders surfing the web and bent on punishing anyone perceived to have insulted the monarchy.

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"There is no better way to punish these people than to socially sanction them," Paiboon Koomchaya, justice minister, said on Tuesday as he pledged to "pursue those people who violate the law".

His message comes amid a growing number of cases of vigilantism by royalist Thais against people accused of insulting the monarchy.

At 10:30am a video was broadcast live on Facebook showing a mob kicking and beating a man and forcing him to prostrate himself in apology for allegedly insulting the monarchy.

During the beating, which appeared to take place in Chonburi, east of Bangkok, the man cried out: "I didn't mean to do it, I love the king! It's my fault."

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Another video widely shared on social media showed an elderly woman on a Bangkok bus being berated by fellow commuters in the presence of police.

As she exits the bus, the woman is slapped in the face by another woman dressed in black.

It is not clear when the incident took place but the video was uploaded on Monday evening.

'Black-shaming'

Thailand's monarchy is protected by a draconian lese majeste law that outlaws criticism with punishments of up to 15 years in jail for each insult uttered.

Prosecutions have surged under the military which seized power two years ago, with record-breaking sentences handed down in some cases.

That has made detailed discussion or debate about the monarchy's role - and its future after Bhumibol's 70-year reign - all but impossible.

WATCH: For Crown or Country: Thailand's Lese Majeste Law

The atmosphere in Bangkok has been overwhelmingly sombre and calm since the death of the king.

But there has been a rise of angry social media calls by royalists for vigilante action against alleged transgressors of "112" - the criminal code that covers the feared law.

On Sunday a woman on Samui island was forced by police to kneel below a portrait of King Bhumibol in front of a baying mob after she allegedly posted an insulting comment about the monarchy on Facebook.

She has since been charged with lese majeste.

Similar mobs have formed on the southern island of Phuket and in nearby Phang Nga province, prompted by alleged comments.

Thailand bids farewell to King Bhumibol

Other social media users have berated those deemed not to be mourning sufficiently deeply or failing to wear black clothes.

The latter phenomenon dubbed "black-shaming" has been condemned by the ruling generals.

Media inside Thailand, both local and foreign, must heavily self-censor. Authorities, however, struggle to censor critics or media based overseas.

But Paiboon said the generals would renew extradition requests for Thais abroad, something that is unlikely to sway governments in countries where lese majeste is not a crime. 

Source: Agence France Presse