The military has reportedly detained hundreds of pro-democracy leaders and activists in Myanmar, including State Counsellor Aung San Suu Kyi and officials in her National League for Democracy, claiming fraud in the election her party won by a landslide last November.
The military took over the country on the day the new parliament was due to convene its first session.
Since then, it has removed 24 ministers and deputies and named 11 replacements, including those for finance, health and foreign affairs.
The National League for Democracy, in a statement on Tuesday, called for the release of Aung San Suu Kyi and the others.
Analysts worry that democracy in Myanmar has been called off yet again.
"The political situation in Myanmar is very unstable right now, Myanmar's democratization process having been suspended. And as the U.S. and other Western countries warn of sanctions, Myanmar could move towards China in terms of foreign policy. I fear the coup could last longer than the year [the military said it would]."
The UN Security Council is convening an emergency meeting on Tuesday to address the long-term threats to peace and security.
U.S. President Joe Biden said Washington will look urgently at reimposing the sanctions that were removed over the past decade based on the country's progress toward democracy.
Japan has urged peaceful dialogue.
South Korea's foreign ministry on Tuesday joined those expressing deep concern.
"The South Korean government respects the aspirations of the people of Myanmar toward democracy as witnessed in last year's general election. We call for the immediate release of State Counsellor Aung San Suu Kyi and the others under detention."
The ministry also said it hopes the issue will be settled peacefuly through democratic procedures.
Kim Jae-hee, Arirang News.