BANGKOK (AFP) - A Thai musician has been sentenced to 15 years in prison for royal defamation, a court official said on Friday, in the latest conviction under a controversial lese majeste law.

The 28-year-old was found guilty of posting insulting messages about the monarchy on Facebook between 2010 and 2011, said a court official from the northeastern province of Ubon Ratchathani, without giving further details.

King Bhumibol Adulyadej, 86, is revered by many Thais and protected by tough royal defamation laws.

Under the strict lese majeste rules anyone convicted of insulting the king, queen, heir or regent faces up to 15 years in prison on each count.

The court sentenced the musician to three years each for nine counts of lese majeste and four months each for 12 counts of violating the computer crime act.

But after admitting to all charges his sentence was reduced to 15 years in jail.

"The suspect had repeatedly committed wrongdoings and in this case the judge has sentenced him with minimum penalties for both charges," said the court official.

Since seizing power in Thailand in May, the army has clamped down on any opposition to its takeover, with a crackdown on perceived slurs against the royals at the heart of its stepped-up online surveillance operations.

Under the rules, anybody can make a complaint about a perceived royal insult and police are duty-bound to investigate.

Before the coup, calls for reform of the lese majeste laws had grown following several high-profile convictions.

But academics urging greater debate are among hundreds of people who were summoned by the junta and temporarily detained in secret locations.