Two young Thais accused of defaming the monarchy in a university play were jailed for two and a half years on Monday, as the ruling junta intensifies a crackdown under a controversial lese majeste law.

Student Patiwat Saraiyaem, 23, and activist Porntip Mankong, 26, had pleaded guilty to defamation following their arrests last August, nearly a year after "The Wolf Bride" -- a satire set in a fictional kingdom -- was performed.

The pair were originally handed five-year jail terms but the sentence was halved due to their confessions, said a judge at Ratchada Criminal Court in Bangkok.

"The court considers their role in the play caused serious damage to the monarchy and sees no reason to suspend their sentences," he told a packed courtroom including the accused, their relatives and friends as well as representatives from the UN human rights office.

Rights groups say lese majeste prosecutions have surged since the army seized power from an elected government last May, as the military seeks legitimacy from its self-designated role as protector of the monarchy.

King Bhumibol Adulyadej, 87, is revered by many in the country as a demi-god and anyone convicted of insulting the king, queen, heir or regent faces up to 15 years in jail on each count.

The pair were charged over their performance of "The Wolf Bride" at Bangkok's Thammasat University to mark the 40th anniversary of a pro-democracy student protest on the campus that was brutally crushed by the military regime in October 1973.

Around a dozen young activists briefly linked hands and chanted slogans in support of the pair and democracy -- defying a junta ban on demonstrations -- as Patiwat, whose feet were bound in chains, and Porntip were led out of the court in handcuffs.

- Suppressing dissent? -

Their lawyer Pawinee Chumsri said her clients, who have been detained since their arrest and denied bail, would not appeal.

Police are hunting for at least six others involved in the play for allegedly violating "112" -- the feared section of the Thai criminal code that contains one of the world's most draconian royal defamation laws.

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Of those on the wanted list, at least two have fled Thailand, joining dozens of academics, activists and political opponents of the junta in self-imposed exile since the coup.

According to the Paris-based International Federation of Human Rights (FIDH) at least 40 people have been arrested since the takeover -- nine of them sentenced to between two and 15 years in prison.

Critics say the lese majeste law has been used as a tool to suppress political dissent, noting many of those charged have been linked to the opposition Red Shirt movement.

Rights activists as well as the media are forced to censor discussion of cases since even repeating details of charges risks breaking the law.

"The Wolf Bride" case is just one of many driven through by the junta in recent months.

"The junta is using the law to bolster its legitimacy with the Thai people," said Paul Chambers, director of research at the Institute of South East Asian Affairs in Chiang Mai.

Previous administrations including that of ousted premier Yingluck Shinawatra have also used the legislation in this way, but the junta has been "even stronger" in asserting its "obedience to the monarchy" through the crackdown, he added.

Andrea Giorgetta from FIDH also said the junta was drawing legitimacy through the monarchy and that the surge in lese majeste cases looked set to continue.

"We're expecting a lot more people to go to jail in the next month. Almost all cases have been backdated (for alleged offences) before the coup," he told AFP. "It's a very grim situation for rights in Thailand."

Analysts say the most recent chapter of Thailand's long-drawn political turmoil is fuelled by anxieties over who will run the country when the more than six-decade reign of the world's longest-serving monarch eventually ends.

Other recent "112" convictions include a taxi driver jailed for two and a half years after his passenger recorded their conversation on a mobile phone, while a student was sentenced to the same period of time for defaming the monarchy in a message posted on Facebook.