U.S. President Joe Biden has threatened to reinstate sanctions in Myanmar after the country's military seized power.
Myanmar's army detained Aung San Suu Kyi and other elected leaders, accusing Ms Suu Kyi's party of fraud over its recent landslide election win.
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 United Nations and the UK have also condemned the coup.
The U.S. 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."
UN Secretary-General Antonio Guterres called the army's move a "serious blow to democratic reforms", as the security council prepared for an emergency meeting. The UN demanded the release of what it said were at least 45 people who had been detained.
In the U.K., Prime Minister Boris Johnson condemned the coup and Aung San Suu Kyi's "unlawful imprisonment".
European Union leaders have issued similar condemnations.
China, which has previously opposed international intervention in Myanmar, urged all sides in the country to "resolve differences". Some regional powers, including Cambodia, Thailand and the Philippines, have said it is an "internal matter".