A 20-year-old Thai student whose father has been detained for ten months under the kingdom's strict lese majeste laws began a hunger strike on Saturday in Bangkok against the controversial legislation.

Activist Somyot Prueaksakasemsuk, the former editor of two now-defunct "Red Shirt magazines, was arrested last April and charged under article 112 of the Thai criminal code over two articles deemed critical of the Thai royals.

His son Panitan, a law student, began his strike on Saturday afternoon in front of Bangkok's criminal court, and was set to fast for 112 hours to highlight the point of law in question.

His protest, which a few dozen people came out to support, comes after the seventh request for his father's bail was denied last month.

"My hunger strike is to call for the right to bail and to show society the injustice on someone who was charged with lese majeste," he told AFP before starting the protest.

He wore a white T-shirt with the message: "Give my dad the right to bail".

Lese majeste carries a penalty of up to 15 years for each count and is designed to protect senior royals from insult, but academics say it has been politicised in recent years.

Many of those charged, like Somyot, have been linked to the "Red Shirt" movement which backed ousted former Prime Minister Thaksin Shinawatra, and other critics of the previous establishment-backed government.

The royal family is an extremely sensitive subject in Thailand, but calls for reform of the law have grown and sparked fierce debate in recent months after several high-profile convictions.

A 61-year-old man was jailed in November for 20 years for sending text messages deemed insulting to the monarchy, while a US citizen in December was also handed two-and-a-half years in prison for allegedly defaming the king.