The junta has also called in dozens of prominent writers and academics and said top political leaders, including deposed prime minister Yingluck Shinawatra, were being held in secret locations without charge to give them ''time to think''.

The rolling crackdown comes as the junta sent thousands of heavily armed troops on to Bangkok’s streets as hundreds of anti-coup protesters defied an order banning gatherings of more than five people.

Protests are also emerging in north and north-east provinces, strongholds of pro-government Red Shirts who have vowed to fight the coup makers.

The junta has arrested 21 people in northern Khon Kaen who they claim are Red Shirt militants and seized three hand grenades, a smoke bomb, ammunition and gas cylinders.

Thai media reported a spike of violence in the country’s south with dozens of bombings that left two people dead and dozens injured. An insurgency has been raging there for years.

More anti-coup protests are planned, creating a serious problem for coup leader General Prayuth Chan-ocha who seized power from Thailand’s democratically elected government last Thursday. Using violence to disperse protesters will turn public opinion against the military but not acting will mean the protests grow.

An army bulletin on television announced the Senate, the only still functioning legislative body, was dismissed, dispelling speculation senators would be allowed to appoint an interim prime minister and administration.

''Responsibility for any laws needing the approval of parliament or Senate will instead be assumed by the leader of the [junta],'' the bulletin said.

The decision was an ominous sign that General Prayuth is digging in for a long-term pervasive takeover without the calling of quick elections.

The junta has threatened to jail for two years any of 150 people it has summoned who refuse the order. It has also ordered seizure of the financial assets of two politicians who have defied it.

Pavin Chachavalpongpun, an associate professor at Japan’s Kyoto University, said he would not return home to the ''crudest form of authoritarianism''.

''To the army chief, I am busy with teaching at the moment,'' he wrote on his Facebook page.

Charupong Ruangsuwan, a leading member of Ms Yingluck’s Pheu Thai Party, said he would not surrender to military figures who had seized power from an elected government. He said he was safe in the country's north.

Pravit Rojanaphruk, a columnist for the English-language The Nation newspaper, who was summoned to report to an army base at 10am on Sunday, was defiant, saying ''the more they exercise their illegitimate power the more illegitimate they become''.

Amid an international outcry over the takeover the US has cancelled a military exercise with Thailand, a long-time close ally in south-east Asia. Military aid, visits by top US military officials and a police training program have also been suspended as the US State Department urged an immediate return to civilian rule, the release of 150 detained political prisoners and a return to democracy.

A State Department official said the US was increasingly concerned about the actions of the Thai military in the days since the coup.

Brad Adams, Asia director at Human Rights Watch, said military rule has thrown Thailand’s rights situation into free fall.

''The army is using draconian martial law powers to detain politicians, activists and journalists, to censor the media and to ban all public gatherings,'' he said.

Among officials seen as serving the ousted government who were purged from their posts were national police chief Adul Saengsingkaew, defence permanent secretary Nipat Thonglek and Tarit Pengdith, head of the Department of Special Investigation, Thailand’s top police agency. Mr Tarit had been in charge of pursuing anti-government leaders on treason charges after their six-month campaign to topple Ms Yingluck’s administration.

General Prayuth, 60, has appointed military commanders to oversee key ministries, raising questions about their ability to handle the complexities of a modern economy that has tipped in recession.

Air force chief Prajin Juntong, who is in charge of economic ministries, will hold a meeting of Finance Ministry officials and bankers on Monday.

General Prayuth told foreign diplomats on Friday he would appoint a reform council that would draft a new constitution and study unspecified ''social changes''.

Foreign tourists in the country, including thousands of Australians mostly in resort areas outside Bangkok, must adhere to a 10pm to 5am curfew, although airports are operating normally.

Australia’s smartraveller.gov.au advises Australians to exercise a high degree of caution in the country and avoid protest rallies. The junta has warned that any foreigners taking part in protests would be arrested and deported.

The junta said it had ordered authorities to ''search websites with agitating content aimed at causing confusion''. The army was ready to ''take action immediately'', the junta said.

Thailand’s King Bhumibol Adulyadej has acknowledged the coup, the junta said. The takeover comes at a time of deep anxiety over the 86-year-old king, who is in ill-health, and the inevitable royal succession.

The coup is seen as part of an eight-year effort by Bangkok’s elite establishment to counter politically powerful Thaksin Shinawatra, a former prime minister whose parties or their proxies have won the last five elections. Mr Thaksin, a billionaire tycoon who lives in exile to avoid a jail sentence for corruption, is Ms Yingluck’s elder brother.