Bangkok: Thailand’s military junta is arresting key Red Shirt supporters of former prime minister Thaksin Shinawatra in their north and north-eastern strongholds in a rolling crackdown that has seen dozens of people detained in secret locations.

The junta on Saturday increased by 35 the number of politicians, writers and academics ordered to report to the military or face arrest. Most of those who have reported have been detained and taken to secret locations. 

Military spokesman Werachon Sukhondhadhpatipak said on Saturday that politicians were detained to give them ‘‘time to think’’.

The military said it would detain ousted government leaders for up to one week.

The arrests come as advisers to Mr Thaksin revealed plans for the setting up of a government in exile to oppose the junta that seized power in a bloodless coup on Thursday.

“Active consideration is being given to the formation of a government in exile in the wake of the illegal seizure of power staged by General Prayuth Chan-ocha,” said Robert Amsterdam, a senior adviser to Mr Thaksin.

Mr Amsterdam said a number of foreign governments have “expressed their willingness to host such a government in exile under internationally established rules and practice".

Mr Thaksin, a billionaire tycoon deposed in a 2006 coup, still wields enormous influence over Thai politics. He is close to Cambodian Prime Minister Hun Sen, raising speculation that a government in exile could be established in neighbouring Cambodia.

“We demand immediate proof from the current junta that Red Shirt leaders and others who were detained remain safe and unharmed,” Mr Amsterdam said in a statement from London.

In a harsher crackdown than the 2006 coup, General Prayuth, 60, appears to be targeting people he believes could mobilise armed opposition to the takeover that has prompted an international outcry.

The Red Shirts have vowed to retaliate. 

However, immediate opposition to the coup has come from hundreds of anti-coup protesters who have taken to the streets of Bangkok and northern Chiang Mai in defiance of a junta order banning gatherings of more than five people. More protests are planned.

Earlier, soldiers ordered the dispersal of anti-government and pro-government protest camps as well imposing a 10pm to 5am curfew, abolishing the constitution, taking television and radio programs off air and imposing strict censorship.

More than 100 political leaders have been detained, including deposed prime minister Yingluck Shinawatra, who is believed to have been taken to a military base outside Bangkok.

Ms Yingluck, Mr Thaksin’s younger sister, was forced from office by a controversial ruling by the Constitutional Court earlier this month.

Core militia Red Shirt leaders are among those detained. 

Military authorities have provided no information on the people who have been arrested, who have no access to lawyers or their families.

“The risk of torture and ill treatment significantly increases when detainees are held incommunicado in unofficial locations and under the control of the military, which lacks training and experience in law enforcement,” Human Rights Watch said.

General Prayuth, a career soldier close to Bangkok’s royalist establishment, was quoted as saying the coup had nothing to do with Thailand’s monarchy.

There is deep anxiety in Thai society about King Bhumibol Adulyadej, 86, who is in ill health, and plans for the royal succession.

General Prayuth said he had drafted a letter informing the king of the coup and submitted it to the king’s private secretary. He said this meant there was no need to seek an audience with King Bhumibol. 

General Prayuth has announced he will push a reform agenda before any elections are held, the key demand of anti-government protesters who have seen parties aligned with Mr Thaksin win the past five of Thailand's democratic elections. 

General Prayuth appointed himself prime minister for the moment and named senior military officers with no experience of governing to oversee ministries, including economic portfolios. The junta said economists would be brought in to advise relevant ministries. 

“There must be reforms in all sectors before the next election that are agreed upon by all parties involved,” he said.

The junta plans to set up a national reform council and appoint a national legislative assembly.

There is speculation General Prayuth may eventually allow anti-Thaksin non-elected senators to appoint an interim prime minister.