A Thai court has sentenced a man to 50 years in jail for comments deemed to have defamed the monarchy - the highest ever sentence handed down under the country's notorious lese majeste law.

Thirty-year-old Mongkol Thirakot was originally sentenced to 28 years for posts he made three years ago on Facebook.

But on Thursday an appeals court added an extra 22 years to the sentence.

The lese majeste law criminalises any negative comment about the monarchy.

The law, which has been widely criticised, is still in force despite the election last year of a civilian government for the first time in 10 years.

At the hearing on Thursday, the judge said he had already reduced Mr Thirakot's sentence by a third because of the defendant's co-operative behaviour.

Details of what prompted such a harsh sentence for Mr Thirakot, an online clothing vendor from Chiang Rai province, have not been published. The judge referred to multiple comments on Facebook, and Thai courts typically pile on additional convictions for each individual post.

The lese majeste law was briefly suspended at the start of the reign of King Vajiralongkorn in 2019, but has been revived and used extensively since the outbreak of unprecedented student-led protests three years ago, which called for sweeping reforms to the monarchy.

An activist and lawyer who first called for a public discussion of the monarchy, Arnon Nampa, also had his jail time increased by four years on Wednesday.

Later in January the Constitutional Court will rule on whether to dissolve Move Forward, the youthful party which won the most votes in last year's general election, over its call to amend the lese majeste law, which some Thai conservatives argue amounts to an attempt to overthrow the entire political order. (BBC)