Thailand’s military will detain former premier Yingluck Shinawatra and ousted government leaders for up to one week, the army says, tightening its grip over the country following a coup that has provoked an international outcry.

Briefing the media for the first time since seizing power on Thursday, the military junta declined to specify where the detainees were held but said they were in no danger, as sporadic protests flared in Bangkok.

“They will be detained for up to one week depending on how directly they were involved (in Thailand’s political turmoil),” army spokesman Colonel Winthai Suvaree told reporters.

In the latest twist to years of escalating political strife, gruff army commander General Prayut Chan-O-Cha deposed the civilian government, acting to prevent the kingdom degenerating into another “Ukraine or Egypt”.

The United States, which has led international calls for restoration of civilian rule, took its first concrete steps, saying it would suspend $US3.5 million ($A3.79 million) in military assistance for the country, about one-third of its aid.

State Department spokeswoman Marie Harf said Washington was considering further cuts. US law mandating suspension of assistance to foreign militaries that overthrow elected governments.

Under the new regime, civil liberties have been drastically curbed, most of the constitution abrogated, and rival political protesters cleared from Bangkok’s streets.

A night-time curfew has tamed the city’s notoriously rowdy night-life, further chilling a vital tourist sector already cooled by the recent strife.

Yingluck and dozens of other figures in the now-deposed government and her Puea Thai party – as well as many of their fierce political rivals – were called in Friday by the army as it corralled potential threats to the overthrow.

“She is under detention, and she is fine,” said Lieutenant General Thirachai Nakwanich, commander of Thailand’s central military region including the capital.

He declined to give her location but said she and others detainees were taken in under a martial law provision allowing the military to hold people for up to seven days without charge.

It was not clear whether any charges were being prepared.

The army said 135 people had so far answered the summons, including Yingluck’s successor, ousted caretaker prime minister Niwattumrong Boonsongpaisan.

Most appear to have been Puea Thai members or allies.

Political analysts view the coup as the culmination of an effort by a Bangkok-based power elite – aligned with the monarchy and military – to eliminate a political threat embodied by Yingluck’s elder brother Thaksin Shinawatra.

Thaksin, a billionaire telecoms tycoon, shook up Thai politics by winning devotion among millions of rural poor with populist measures, catapulting him to prime minister in 2001 polls.

He was deposed in 2006 in a military coup, fleeing abroad two years later to avoid a corruption conviction, but his family and allies continued to triumph at the ballot box as political temperatures rose.

The constitution was replaced after 2006 with one intended to curb Thaksin’s electoral influence.

Anti-Thaksin forces – alleging corruption in Yingluck’s administration – have staged months of deadly Bangkok protests, triggering rival demonstrations by the pro-Thaksin “Red Shirt” movement.

The tensions spiralled in early May with Yingluck’s dismissal from office in a controversial court ruling that set the stage for Thursday’s takeover.

Sporadic demonstrations denouncing the takeover have occurred in Bangkok, although no clashes have been reported.

The takeover has brought a mixed reaction from Thais, with some protest-fatigued Bangkok residents expressing hope it will bring stability, while others lamented the threat to democracy.

Thailand’s democratic development has now been interrupted by 19 actual or attempted coups since 1932, interventions that traditionally require the monarchy’s approval.

It was unclear whether 86-year-old King Bhumibol Adulyadej had blessed Prayut’s takeover.