Eight Thai politicians are facing charges of sedition and for spreading "false information" about the draft constitution, local reports said, a development that creates "a climate of fear" in the country ahead of a referendum, according to a rights group.
Deputy Prime Minister Prawit Wongsuwan said on Thursday that the politicians, who are loyalists of former Yingluck Shinawatra, would be tried in a military court, and that their detention would continue for at least a week.
But those who were detained, including a suspended provincial chief and a former member of parliament, told local media that the letters distributed to their supporters were only expressing "opinions" about the proposed new charter, which seeks to return the country to civilian rule in 2017.
A referendum on the new constitution is scheduled for August 7.
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The members of the Pheu Thai Party from the northern Chiang Mai province were taken in military custody on Wednesday. Their party is headed by Yingluck, who was ousted by the military in 2014. Yingluck's brother Thaksin also served as prime minister before being ousted by a similar coup in 2006.
Among those who will be charged are Boonlert Buranupakorn, the suspended president of the Chiang Mai provincial administrative organisation, his niece Tasanee Buranupakorn, a former member of parliament from Chiang Mai, and her sister, Thanthip.
They all belong to the Buranupakorn family, a major supporter of the former ruling party, whose stronghold includes the Chiang Mai province and the city of the same name.
Earlier, Boonlert was ordered suspended by Prime Minister Prayuth Chan-ocha for his alleged role in distributing the letter discussing details of the proposed constitution. He is said to be traveling abroad.
'Unjustified arrests and charges'
In a statement to Al Jazeera, Human Rights Watch (HRW) said the arrests showed that Thailand's military "junta" officials "desperately want to win the vote".
"These arrests, and hauling the suspects into military detention, absolutely contravenes Thailand's international human rights obligations. The charge of sedition is being used like a hammer to pound anyone that says things the military junta doesn't like," Brad Adams, HRW's Asia director, said.
Adams also called on the UN and member countries "to publicly condemn" the arrests, and demand the government "end its campaign of repression".
According to local media reports, the week-long detention period of the local politicians was ordered by the National Council for Peace and Order (NCPO).
Prawit, who is also in-charge of the country's defence ministry, told reporters on Wednesday that there was "substantial evidence" to file the charges.
But Tasanee, the former MP, denied the government allegations.
"I am confident the letters, which were used to accuse me contain no information which breach the laws. No efforts have been made to distort or falsify the draft charter," Tasanee was quoted by the Bangkok Post as saying on Wednesday.
More than 50 million registered voters are expected to vote in next month's referendum on the country's 20th constitution, which was drafted by the military.
