By Khettiya Jittapong and Andrew R.C. Marshall
BANGKOK (Reuters) - Human Rights Watch expressed "grave concerns" on Saturday for the safety of a factory worker in Thailand arrested and taken to an undisclosed location for allegedly criticising the country's monarchy and junta.
Thanakorn Siripaiboon, 27, was arrested on Dec. 8 for sharing Facebook posts about government corruption and pressing "like" to an image deemed insulting to Thailand's king, the New York-based group said in a statement.
"Since then, the police, the military, and the corrections department have all denied knowledge of Thanakorn's whereabouts to his family and lawyers, raising grave concerns for his safety," said Human Rights Watch.
Thailand's strict lese majeste laws punish anyone who "defames, insults or threatens the king" or other senior royals. The Thai military, which seized power in May 2014, treats it as a threat to national security, and at least 54 people have been charged during military rule.
Those accused of lese majeste are tried in military courts, which have handed down record jail sentences.
In August, a political opponent of the junta was sentenced to 60 years for six Facebook posts. It was halved to 30 after he pleaded guilty.
Two suspects recently died in military custody during a police investigation of corruption allegations involving nationwide events aimed at celebrating the monarchy.
Thai police spokesman Dejnarong Suthicharnbancha told Reuters that Thanakorn, the factory worker, had been detained by the military under section 44, a sweeping security provision that allows detention without charge for seven days.
Thanakorn would then be sent to police to be charged, said Dejnarong. "No worries, we'll take good care of him," he said.
He would not disclose Thanakorn's whereabouts. Nor would Winthai Suvaree, a spokesman for the National Council of Peace and Order, as Thailand's ruling junta is formally known.
He said the army was still questioning Thanakorn and would deliver him to police after seven days.
According to Human Rights Watch and Thai media reports, one Facebook post shared by Thanakorn involved a military-built park which the junta itself is investigating for alleged corruption.
"Thanakorn's secret detention should set off flashing red lights ? especially since the Thai authorities failed to resolve two recent deaths of detainees in military custody," said Brad Adams, Asia director at Human Rights Watch.
"Thailand's junta has increasingly flouted international legal protections by holding civilian detainees incommunicado in military camps."
King Bhumibol Adulyadej, 88, is the world's longest-reigning monarch. His health is fragile and he has not appeared in public for months.
(Additional reporting by Manunphattr Dhanananphorn; editing by Andrew Roche)