Teachers and students in Myanmar rallied on Friday to a growing civil disobedience campaign as the anti-coup protest movement won the support of ousted leader Aung San Suu Kyi's party.
Stepping up measures to quell discontent, police arrested one of Suu Kyi's veteran aides and dozens of people who had joined noisy demonstrations against Monday's coup.
International pressure on the junta increased with the UN Security Council urging the release of detainees and Washington considering sanctions on the ruling generals.
Teachers became the latest group to join a civil disobedience campaign with some lecturers refusing to work or cooperate with authorities over the coup that halted a long and unsteady transition to democracy.
"We want the military coup to fail," said lecturer Nwe Thazin Hlaing at the Yangon University of Education.
Reuters was unable to reach the government for comment.
The disobedience campaign, which began with doctors, has also spread to some government offices and on Friday won the formal backing of Suu Kyi's National League for Democracy party.
In a statement, the party denounced the coup and Suu Kyi's detention as "unacceptable" and said it would help people who are arrested or sacked for opposing the takeover.
Army chief Min Aung Hlaing took power citing alleged irregularities in a November election that the party won in a landslide. The electoral commission has said the vote was fair.
There has been no outpouring of people onto the streets in a country with a bloody history of crackdowns on protests, but there were signs of coup opponents growing bolder - with dozens of youths parading in the southeastern city of Dawei.
In the biggest city, Yangon, supporters hung red clothing, ribbons and balloons outside their homes to show support.
"We put red balloons down the whole street," said Myint Myint Aye, 49. "This is a non-violent campaign. We want to show the dictators that all of us are with Mother Suu."
But authorities also began to step up action against coup opponents.
In Myanmar's second city of Mandalay, 30 people were arrested over pot-banging protests which have taken place for the last three nights.
Eleven Media quoted Maung Maung Aye, deputy head of the regional police force, as saying they were accused of breaking a law against "causing noise in public streets".
The latest high-profile detainee was 79-year-old Win Htein, a stalwart of Suu Kyi who was repeatedly imprisoned during their decades of struggling against previous juntas.
"I have never been scared of them because I have done nothing wrong my entire life," he told Reuters by phone as he was taken away.
Reuters was unable to reach police for comment on his arrest or what charges could be brought against him.
The 15-member UN Security Council released a statement on Thursday calling for the release of all detainees and for respect for human rights, fundamental freedoms and the rule of law.
But before it won consensus among members that include China and Russia, which have close ties to Myanmar's army, the language of the draft was changed to remove any mention of a coup.
Nobel Peace laureate Suu Kyi, 75, has not been seen since her arrest in morning raids on Monday. Police have filed charges against her for illegally importing and using six walkie-talkie radios found at her home.
President Joe Biden said the United States was working with allies and partners to address the generals' takeover.
"There can be no doubt in a democracy force should never seek to overrule the will of the people or attempt to erase the outcome of a credible election," he said.
National security adviser Jake Sullivan said targeted sanctions on individuals and on entities controlled by the military were under consideration.
He spoke by phone with ambassadors from the Association of South East Asian Nations (ASEAN) regional bloc. Indonesia and Malaysia later said regional foreign ministers would be asked to hold a special meeting on the situation.
Myanmar's generals have few overseas interests that could be targeted by sanctions, but the military has extensive business interests that could suffer if foreign partners leave.
Japanese drinks giant Kirin Holdings said on Friday it was terminating its alliance with a top Myanmar conglomerate whose owners, according to the United Nations, include members of the military. Kirin said the coup had "shaken the very foundation of the partnership".