BANGKOK (Reuters) - Thailand faces a "moment of shame" when the United Nations Human Rights Council reviews its rights record on Wednesday (May 11), a rights group said, amid fresh arrests of online critics accused of criticising the junta.

The crackdown comes as Thailand's military government prepares to put a widely criticised military-written constitution to the public in August.

The military seized power in a May 2014 coup saying it had to end a bitter cycle of political unrest that had rocked Thailand since 2006 when the army ousted former prime minister Thaksin Shinawatra.

Rights groups say the junta has tightened its grip on power and severely repressed rights in the past year. It has jailed critics, introduced new laws aimed at curbing freedom of speech, censored the media and restricted political debate.

The Universal Periodic Review (UPR) is a cyclical review of the human rights record of the 193 United Nations member states.

Thailand, which was last reviewed in 2011, is one of 14 countries being questioned by the UPR working group in the current session, which ends on Friday.

"It will be a moment of shame for the Thai government at a major international forum where Thailand once was honoured and respected," Mr Sunai Phasuk, Thailand researcher for Human Rights Watch, told Reuters. "I hope it will send a clear message back to Bangkok that they immediately have to reverse their course."

Colonel Winthai Suvaree, a spokesman for the junta, said it wants the Thai delegation to "tell the truth about what is happening in Thailand".

On April 27, troops arrested eight activists over Facebook comments critical of the junta and the draft Constitution.

The eight were released on bail on Tuesday.

Two of the eight face separate charges of royal insult. They were charged on Wednesday with insulting the revered monarchy in private Facebook messages, the latest in a growing number of royal insult charges under the junta.

"We have additionally charged them with royal defamation and computer crimes," Police Lieutenant-Colonel Chaiporn Nittayapat, who is in charge of the case, told Reuters.

Issues raised in documents seen by Reuters submitted to the UN by rights groups and UN member countries include the expansion of internal policing powers for the military and the use of military courts to try critics.

More than a decade of political strife has seen at times violent street protests by both Thaksin's supporters and their opponents.