Myanmar police fired stun grenades to disperse protesters in the city of Yangon on Tuesday, witnesses said, as foreign ministers of neighbouring countries were due to hold talks with the military in an effort to quell deadly violence.

The talks will come two days after the bloodiest day of unrest since the military removed Aung San Suu Kyi's elected government a month ago, unleashing anger and mass street protests across Myanmar.

Protesters, many wearing hard hats and clutching makeshift shields, had gathered behind barricades in different parts of Yangon to chant slogans against military rule.

Crowds also gathered in other parts of the country, media reported.

"If we're oppressed, there will be explosion. If we're hit, we'll hit back," the crowd chanted at one Yangon protest before police moved in to break up it up with stun grenades, witnesses said.

There were no reports of any injuries.

At least 21 protesters have been killed since the turmoil began. The army said one policemen was killed.

The coup on Feb. 1 halted Myanmar's tentative steps towards democracy after nearly 50 years of military rule, and has drawn condemnation and sanctions from the United States and other Western countries, and growing concern among its neighbours.

Singapore Foreign Minister Vivian Balakrishnan said his counterparts in the Association of Southeast Asian Nations (ASEAN) would be frank when they meet by video call on Tuesday and will tell a representative of Myanmar's military they are appalled by the violence.

In a television interview late on Monday, Balakrishnan said ASEAN would encourage dialogue between Suu Kyi and the junta.

"They need to talk, and we need to help bring them together," he said.

ASEAN groups Myanmar, Singapore, the Philippines, Indonesia, Thailand, Laos, Cambodia, Malaysia, Brunei and Vietnam.

The military justified the coup saying its complaints of fraud in a November election won by Suu Kyi's party were ignored. The election commission said the vote was fair.

Junta leader Senior General Min Aung Hlaing, in remarks read on state television by a newscaster, said protest leaders and "instigators" would be punished and threatened action against civil servants refusing to work.

Min Aung Hlaing has pledged to hold new elections and hand power to the winner but has given no time frame.

'UTTERLY UNACCEPTABLE'

ASEAN's effort to engage with Myanmar's military has been criticised by supporters of democracy, with a committee of ousted Myanmar lawmakers declaring the junta a "terrorist" group and saying ASEAN's engagement will give it legitimacy.

Sa Sa, the committee's anointed envoy to the United Nations, said ASEAN should have no dealings with "this illegitimate military-led regime".

The alumni of ASEAN youth programmes in Myanmar said the bloc should be talking to the international representatives of Suu Kyi's administration, not to the regime.

"ASEAN must understand that the coup or the re-election promised by the military junta is utterly unacceptable to the people of Myanmar," it said it a letter to ASEAN.

Philippine Foreign Minister Teodoro Locsin indicated on Twitter that ASEAN would be firm with Myanmar and said the bloc's policy of non-interference in members' internal affairs "is not a blanket approval or tacit consent for wrong to be done there".

Suu Kyi, 75, appeared at a court hearing via video conferencing on Monday and looked in good health, one of her lawyers said. Two more charges were added to those filed against her after the coup, the lawyer said.

The Nobel Peace laureate has not been seen in public since her government was toppled and she was detained along with other party leaders.

Hundreds of people have been arrested since the coup, according to activists, the latest a journalist for the Democratic Voice of Burma, who live-streamed security forces outside his apartment on Monday in the coastal town of Myeik, where he had been filming protests. DVB confirmed the arrest.

The United States warned Myanmar's military on Monday that it would take more action if security forces kill unarmed people and attack journalists and activists, which State Department spokesman Ned Price called "abhorrent violence".

White House Press Secretary Jen Psaki said the Biden administration was preparing further costs on those responsible for the coup.

U.S. Ambassador to the United Nations Linda Thomas-Greenfield said she hoped to use Washington's presidency of the United Nations Security Council in March to push for more "intense discussions" on Myanmar. 

(Reporting by Reuters Staff; Additional reporting by Aradhana Aravindan in Singapore, Michelle Nichols at the United Nations, Steve Holland, Alexandra Alpe, Humeyra Pamuk, Daphne Psaledakis and Simon Lewis in Washington; Writing by Martin Petty and Rob Birsel; Editing by Raju Gopalakrishnan and Stephen Coates) ((martin.petty@tr.com; +66 89 607 0413))