PHNOM PENH (Reuters) - A 50-year-old teacher has been arrested in Cambodia for allegedly insulting the monarchy in a comment posted on Facebook, police said on Sunday, the first such arrest since the country adopted a royal insult law earlier this year.

Cambodia’s parliament unanimously adopted a law in February, that forbids insulting the monarchy.

Rights groups expressed concern that such legislation, already in effect in neighboring Thailand, could be used against critics of the government.

Police in the central province of Kampong Thom arrested Kheang Navy, a primary school principal, over comments he made that were allegedly critical of King Norodom Sihamoni, his father, late King Norodom Sihanouk and his half-brother Prince Norodom Ranariddh over their alleged role in the dissolution of the main opposition Cambodia National Rescue Party (CNRP). “He is being detained,” Nhem Chhunly, a police chief in the province, told Reuters. “He admitted to police that those were his comments,” Nhem Chhunly said, adding that he did not know when Kheang Navy would be sent to court to face charges.

Reuters was unable to reach Kheang Navy, who is in police custody, for comment. He has not yet been appointed a lawyer.

Cambodia’s lese-majeste law stipulates that a prosecutor can file a criminal suit on behalf of the monarchy against anyone deemed to be insulting the royal family.

Those found guilty would face between one and five years in prison and a fine of between $500 and $2,500. King Norodom Sihamoni is officially Cambodia’s head of state, but long-serving Prime Minister Hun Sen has ruled for 33 years. Last year, the opposition CNRP was dissolved at the government’s request and its leader, Kem Sokha, arrested on treason charges that he says were politically driven. The crackdown comes ahead of a July 29 general election in which Hun Sen will be largely unchallenged.

In neighboring Thailand, lese-majeste cases have increased since the military took control following a 2014 coup.

The junta has vowed to use harsh measures against perceived critics of the country’s royal family.

Thailand has some of the world’s toughest lese-majeste laws. Those found guilty face up to 15 years in prison for each offence.