Naypyitaw: Myanmar military television says the military has taken control of the country for one year.
An announcer on military-owned Myawaddy TV made the announcement Monday morning.
State Counsellor Aung San Suu Kyi was detained under house arrest, reports said, as communications were cut to the capital.
Phone and internet access to Naypyitaw was lost and Suu Kyi's National League for Democracy party could not be reached.
The U.S., Australia and others were concerned by the reports and urged Myanmar's military to respect the rule of law.
The United States is alarmed by reports that the Burmese military has taken steps to undermine the country's democratic transition, including the arrest of State Counselor Aung San Suu Kyi and other civilian officials in Burma, White House spokesperson Jen Psaki said in a statement from Washington. She said President Joe Biden had been briefed on the reported developments.
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, the statement said. Burma is the former name of Myanmar.
Australian Foreign Minister Marise Payne called for the release of Suu Kyi and others reported to be detained. We strongly support the peaceful reconvening of the National Assembly, consistent with the results of the November 2020 general election, she said.
Myanmar lawmakers were to gather Monday in the capital Naypyitaw for the first session of Parliament since last year's election.
Online news portal Myanmar Now cited unidentified sources about the arrest of Suu Kyi and the NLD's chairperson around dawn and did not have further details. Myanmar Visual Television and Myanmar Voice Radio posted on Facebook around 6:30 a.m. that their programs were not available to broadcast regularly.
The 75-year-old Suu Kyi is by far the country's most dominant politician, and became the country's leader after leading a decades-long nonviolent struggle against military rule.
Suu Kyi's party captured 396 out of 476 seats in the combined lower and upper houses of Parliament in the November polls, but the military holds 25% of the total seats under the 2008 military-drafted constitution and several key ministerial positions are also reserved for military appointees.
The military, known as the Tatmadaw, charged that there was massive voting fraud in the election, though it has failed to provide proof. The state Union Election Commission last week rejected its allegations.
Amid the bickering over the allegations, the military last Tuesday ramped up political tension when a spokesman at its weekly news conference, responding to a reporter's question, declined to rule out the possibility of a coup. Maj. Gen. Zaw Min Tun elaborated by saying the military would follow the laws in accordance with the constitution.
Using similar language, Commander-in-Chief Senior Gen. Min Aung Hlaing told senior officers in a speech Wednesday that the constitution could be revoked if the laws were not being properly enforced. Adding to the concern was the unusual deployment of armored vehicles in the streets of several large cities.
On Saturday, however, the military denied it had threatened a coup, accusing unnamed organizations and media of misrepresenting its position and taking the general's words out of context.
On Sunday, it reiterated its denial, this time blaming unspecified foreign embassies of misinterpreting the military's position and calling on them not to make unwarranted assumptions about the situation.