US President Joe Biden has threatened to reinstate sanctions on Myanmar after the country's military seized power.
Sanctions had only recently been eased, after the country began emerging from a decades-long military dictatorship.
On Monday, Aung San Suu Kyi and other elected officials were detained, with Ms Suu Kyi's party accused of fraud over its landslide election win.
The UN, the UK and the EU have also condemned the military takeover amid fears of potential protests and unrest.
Ms Suu Kyi - who spent nearly 15 years in detention between 1989 and 2010 - has urged her supporters to "protest against the coup" in a letter written before she was detained. It warned the military's actions would put the country back under a dictatorship.
The military has refused to accept November's election results, declaring a year-long state of emergency. It has already replaced 11 ministers and deputies, including in finance, health, the interior and foreign affairs.
But in a statement, Mr Biden said "force should never seek to overrule the will of the people or attempt to erase the outcome of a credible election".
The US had removed sanctions over the past decade as Myanmar progressed to democracy. Mr Biden said this would be urgently reviewed, adding: "The United States will stand up for democracy wherever it is under attack."
However, it is unclear how much effect his words will have on Myanmar's military. Toe Zaw Latt, Myanmar bureau chief of the Democratic Voice of Burma (DVB), told the BBC that the military will know sanctions are an unavoidable consequence of their actions, adding that "they don't care about Western sanctions" and are more concerned "about how China, Japan, South Korea respond".
China, which has previously opposed international intervention in Myanmar, urged all sides in the country to "resolve differences". Other countries in the region, including Cambodia, Thailand and the Philippines, have said it is an "internal matter".