Anti-coup protesters on Thursday took to the streets of Myanmar for a sixth consecutive day, after US President Joe Biden announced sanctions against the Southeast Asian nation's generals and demanded they relinquish power.

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.

"Don't go to the office," chanted a group of protesters outside Myanmar's central bank in Yangon, part of a civil disobedience 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 bank employee who had joined the protest told AFP.

There were also fresh rallies 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 of 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.

"This seems like a well calibrated set of measures... Also a strong signal that President Biden himself announced them," Myanmar-based political analyst Richard Horsey tweeted, describing the sanctions as a "clear message" to the military.

- Crackdown deepens -

There were more reports of arrests on Thursday, including the deputy speaker of the parliament's lower house and a key aid 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 the November 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 masses of people taking to the streets.

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.

"They can shoot a young woman but they can't steal the hope and resolve of a determined people," UN special rapporteur Tom Andrews tweeted Wednesday.

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 cyber security 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.