“The NCPO’s action against the suspects has deprived them of their rights and liberties because it has accused them of violating Article 116 of the security law,” he said.

The junta’s drastic action stemmed from their fear that the charter would fail to pass the referendum. The military should release them on bail to fight the charges, he said.

Key Pheu Thai politicians saw their request to meet with former Pheu Thai MP Thassani Buranupakorn and the six others turned down. The seven have been detained for questioning on suspicion of violating the referendum law and committing criminal association.

They had dropped by the 11th Army Circle in Bangkok to visit Thassani.

The politicians were told to submit a formal request for a visit the next day.

Besides Chaturon, former commerce minister Wattana Muangsook and former deputy prime minister Pongthep Thepkanchana were among the group.

Salil Shetty, secretary-general of Amnesty International, called on Prime Minister Prayut Chan-o-cha to take measures to ensure that people can exercise their rights freely and peacefully without fear of suppression in regard to the August referendum.

“In particular, I urge you to allow individuals to freely receive and impart information,” he said in an open letter.

The public should also be allowed “to engage in public debate and campaigns concerning the draft constitution, to peacefully gather and demonstrate, and to express dissenting viewpoints”, he said.

Chamnong Chaimongkiol, the attorney for Thassani’s family, said Thassani had not been formally charged and he would like to post the bail for her release, citing her health problems from stress, a thyroid condition and a urinary tract infection.

Deputy Prime Minister Prawit Wongsuwan denied allegations that the government had targeted the famous business clan in Chiang Mai because they belonged to a rival political camp.

“We do not harass anyone. We do everything according to evidence. The case is being investigated by police, the military and administrative officials working together,” he said.

The action against the Buranupakorn family was not a case of “killing a hen before the monkeys”, a Thai proverb that means “killing one to warn a hundred”.

“Anyone committing any offence will face action. No one knew there would be such an incident inChiang Mai,” he said.

A source said Boonlert Buranupakorn would turn himself in today at the 11th Army Circle.

Kritsada Bunrat, permanent secretary of the Interior Ministry, circulated urgent letters to governors across the country for them to support the public relations campaigns in their provinces for the charter referendum and ensure no offences under the public referendum law are committed.

Maj-General Kongcheep Tantrawanit, spokesman for the Defence Ministry, said Prawit had ordered all military units under the ministry to scrutinise social media messages that deviate from the truth or stir up panic among the public.

They were instructed to check the source of the messages and urge the public to be aware of false information going viral.

Pol Maj-General Ampol Buarabporn, chief of the Chon Buri provincial police, presided over the send-off ceremony of 320 police and volunteers to crack down on criminals and vices in Pattaya ahead of the August 7 referendum.

The officials will target those dealing in illicit drugs, possessing guns and war weapons and trading in contraband.