Pressure has mounted on the military junta that seized power in Myanmar this week, with closed-door UN talks on the crisis, criticism from the US, Britain and others, and the prospect of sanctions against the South-East Asian country.
Calls increased on Tuesday for the release of Aung San Suu Kyi, the leader of the democratically elected government, and others detained when the army seized power early on Monday while claiming fraud in last November's elections.
A US State Department official said on Tuesday that Ms Suu Kyi's government was "deposed in a military coup", meaning Washington would cut assistance to Myanmar's government and pave the way for potential sanctions.
"We continue to call on the Burmese military leadership to release them and all other detained civil society, and political leaders immediately and unconditionally," the official told reporters.
The UN Security Council met behind closed doors on Tuesday to hear from Christine Schraner Burgener, the UN envoy to Myanmar for talks involving regional heavyweights China and Russia.
UN Secretary General Antonio Guterres called the coup a "serious blow to democratic reforms" that have been reshaping Myanmar since the armed forces passed control to a nominally civilian government in 2011.
The UN also said the coup may worsen the plight of about 600,000 Rohingya Muslims in Myanmar who suffered widespread abuses in a 2017 military crackdown. Rohingya refugees living in camps in Bangladesh say they are now less likely to return home.
Nigel Adams, a junior British foreign minister, said on Tuesday that Ms Suu Kyi and her National League for Democracy party were "rightful winners of the election" and called for the release of the Nobel Peace Prize winner.
Amnesty International and Human Rights Watch have called for the restoration of civilian rule, the release of detainees and for the UN to slap sanctions on Myanmar's military chiefs.
In Myanmar's biggest city, Yangon, locals banged pots and pushed car horns in noisy protests on Tuesday over the military coup in video footage and live-streams shared over social media, Reuters said.
Myanmar’s army said on Monday it had detained Ms Suu Kyi and others in response to “election fraud”, handing power to military chief Min Aung Hlaing and imposing a year-long state of emergency. Ms Suu Kyi’s party won 83 per cent of the vote in the elections.
The US State Department decision, announced on a call with reporters, is the first major foreign policy declaration by the Biden team on Asia since President Joe Biden took office on January 20.
"A very small circle of Burma's military leaders have chosen their own interests over the will and well-being of the people,” the official added.