Australia has expressed deep concern as the Myanmar military again seizes control of the country in a coup.
Myanmar leader Aung San Suu Kyi and other senior figures from the ruling party have been detained in early morning raids.
The military has since declared a one-year state of emergency.
The arrests come after days of escalating tension between the civilian government and powerful military.
Australian Foreign Minister Marise Payne is alarmed at the developments.
"Australia is a longstanding supporter of Myanmar and its democratic transition," she said on Monday.
"We call 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 have been detained unlawfully."
Prime Minister Scott Morrison described the situation in Myanmar as disturbing.
"We have been a long standing supporter of Myanmar's democratic transition, including the election in November," he told reporters in Canberra.
Australia and international allies released a joint statement on Friday opposition any efforts to alter the election outcome and urging the military to adhere to democratic norms.
"We all hope for what I know the Myanmar people want to achieve," Mr Morrison said.
The federal opposition has also condemned the actions of the Myanmar military.
"Labor condemns the detention of numerous political and civil society figures in Myanmar. This is a direct attack on Myanmar's ongoing democratic transition," Senator Penny Wong said.
"We look to the Australian government to make clear our expectations that democratic norms are respected and strengthened."
Fears of an attempted coup have grown in the aftermath of an election the army claims was fraudulent.
Myo Nyunt, a spokesman for the governing National League for Democracy, told Reuters that Aung San Suu Kyi, President U Win Myint and other leaders were taken in the early hours of the morning.
"I want to tell our people not to respond rashly and I want them to act according to the law," he said, adding he also expected to be detained.
Phone lines to Naypyitaw, the capital, were not reachable in the early hours of Monday.
A military spokesman did not answer phone calls seeking comment.
An NLD lawmaker, who asked not to be named for fear of retaliation, said another of those detained was Han Thar Myint, a member of the party's central executive committee.
Political tension soared last week after a spokesman for the military, which had ruled Myanmar for five decades, said a coup could not be ruled out if its complaints of widespread fraud were ignored.
The commander-in-chief, Senior General Min Aung Hlaing, told senior officers the constitution could be revoked if the laws were not being properly enforced.
Military officials later denied their chief had threatened to stage a coup, saying the media had misinterpreted his words.
Adding to the concern was the unusual deployment of armoured vehicles in the streets of several large cities.
The ruling National League for Democracy party captured 396 out of 476 seats in the November 8 election, allowing it to form a government led by Suu Kyi for another five years.
The military-backed Union Solidarity and Development Party won only 33 seats.
The military has publicly complained several times of mass electoral fraud and called for an official review of the results.
Australian Associated Press