The United Nations-led condemnation of Myanmar's military on Monday after it seized power, calling for the release of elected leaders, including Nobel laureate Aung San Suu Kyi.
UN Secretary-General Antonio Guterres said the developments were a "serious blow to democratic reforms" and urged all leaders to refrain from violence and respect human rights, a UN spokesman said.
The United States, Australia and Singapore expressed dismay at the military's declaration of a state of emergency and the detentions, which the army said it had carried out in response to "election fraud".
"We call on Burmese military leaders to release all government officials and civil society leaders and respect the will of the people of Burma as expressed in democratic elections on November 8," US Secretary of State Antony Blinken said in a statement.
The White House said US President Joe Biden had been briefed on the detentions.
"The United States opposes any attempt to alter the outcome of recent elections or impede Myanmar's democratic transition, and will take action against those responsible if these steps are not reversed," White House spokeswoman Jen Psaki said.
Australian Foreign Minister Marise Payne called on the military "to respect the rule of law, to resolve disputes through lawful mechanisms and to release immediately all civilian leaders and others" who had been detained.
Singapore's Foreign Ministry urged all parties to exercise restraint and work towards a positive and peaceful outcome.
The detentions came after days of escalating tension between the civilian government and the military after the November 8 election in which Suu Kyi's National League for Democracy (NLD) scored a landslide win.
The army on Monday handed power to military chief Min Aung Hlaing and imposed a state of emergency for one year, according to a statement on a military-owned television station.