Myanmar police filed charges against ousted leader Aung San Suu Kyi on Wednesday (February 3) for illegally importing communications equipment.
And she will be detained until February 15 for investigations, a police document showed.
Pots and pans clanged in protest in Yangon, Myanmar's biggest city, and honking car horns marked the first widespread protest against this week's military coup.
Nobel Peace laureate Suu Kyi and other politicians were arrested on Monday (February 1), cutting short Myanmar's long transition to democracy.
Some shouted "evil be gone", a traditional gesture to drive out evil or bad karma.
The army has refused to accept the election victory of Suu Kyi and her National League for Democracy party, which won by a landslide last November.
It has alleged electoral fraud and imposed a state of emergency.
The G7 condemned the coup on Wednesday and said the election result must be respected.
China has not specifically condemned the coup in the neighboring country but its foreign ministry rejected the suggestion that it supported or gave tacit consent to it.
Accusations filed by police against Suu Kyi said six illegally imported walkie-talkie radios were found in a search of her home in the capital Naypyidaw.
A separate document showed police filed charges against ousted President Win Myint for violating protocols to stop the spread of coronavirus during the campaigning for the election.
Late Tuesday, a senior party official said he learned that Suu Kyi was under house arrest in Naypyidaw and was "in good health", but would not be moved.
Also on Wednesday, 70 hospitals and medical departments across Myanmar stopped work to protest against the coup, according to a statement posted on Facebook.