There has been an outpouring of anger and defiance since the military ousted civilian leader Aung San Suu Kyi last week and detained her along with other senior figures of her National League for Democracy party.

Security forces have used tear gas, water cannon and rubber bullets against the protesters, with isolated reports of live rounds also being fired. Police also ramped up their harassment of the NLD with a raid on its headquarters.

But demonstrators again marched peacefully on Thursday in Naypyidaw -- the capital and military stronghold -- as well as Yangon, the largest city and commercial hub, which saw tens of thousands flood into the streets.

"Don't go to the office," chanted a group of protesters outside Myanmar's central bank in Yangon, part of an effort urging civil servants and people in other industries to boycott work and put pressure on the junta.

"We aren't doing this for a week or a month -- we are determined to do this until the end when (Suu Kyi) and President U Win Myint are released," one protesting bank employee told AFP.

Joining the protest were dozens from the ethnic Karen, Rakhine and Kachin minority groups, marching down Yangon's main Myaynigone junction.

"Our ethnic armed groups and ethnic people have to join together to fight against the military dictatorship," Saw Z Net, an ethnic Karen protester and sound engineer, told AFP.

There are more than 130 ethnic minority groups across Myanmar, some of whom have been forced to flee their homes due to clashes between the military and ethnic armed groups, who agitate for autonomy in various states.

Fresh rallies also cropped up in the cities of Dawei and Mandalay, with protesters carrying signs that said "Restore our Democracy!" and "We condemn the military coup".

- US sanctions -

Western nations have repeatedly denounced the coup, with the United States leading calls for the generals to relinquish power.

In the most significant concrete action to pressure the junta, Biden announced Wednesday that his administration was cutting off the generals' access to $1 billion in funds in the United States.

"I again call on the Burmese military to immediately release democratic political leaders and activists," Biden said, as he flagged further sanctions.

"The military must relinquish power."

European Union foreign policy chief Josep Borrell has also warned the bloc could impose fresh sanctions on Myanmar's military.

- Crackdown deepens -

There were more reports of arrests Thursday, including the deputy speaker of the parliament's lower house and a key aide to Suu Kyi, taking the number of coup-linked detentions to more than 200, according to monitor Assistance Association for Political Prisoners.

The military justified last week's power grab by claiming widespread voter fraud in November's polls, which saw a landslide for Suu Kyi's party.

It quickly moved to stack courts and political offices with loyalists as it ended a decade of civilian rule.

Fears are growing over how long the junta will tolerate the protests.

Live rounds were fired at a rally in Naypyidaw this week, critically wounding two people -- including a woman who was shot in the head.

Images depicting the woman have been shared widely online alongside expressions of grief and fury.

The military's clampdown on information using internet blackouts -- with tech companies ordered to cut communications intermittently -- has drawn widespread condemnation.

Concern was also building Thursday that the junta was planning to impose a much harsher and sustained internet crackdown.

Tech-focused Myanmar civil society organisation MIDO tweeted that a draft cybersecurity bill had been sent to telecom companies, which would allow the military to order blackouts and website bans.

It would also require social media platforms to hand over users' metadata.

Norway-based Telenor, which had complied last to block social media platforms where an online anti-coup campaign was proliferating, said it was reviewing the law.