At least 38 protesters were killed on Sunday as security forces cracked down on anti-coup protesters, taking the total death toll to more than 120, according to the Assistance Association for Political Prisoners (AAPP) monitoring group.

Protesters demanding the release of Suu Kyi and the restoration of democracy have taken to the streets across Myanmar every day for around six weeks despite the junta's increasingly forceful attempts to quell the dissent.

Sunday -- the joint deadliest day of unrest along with March 3 -- saw violent clashes between security forces and protesters and the torching of several Chinese-owned factories in a textile-producing district of Yangon, as many protesters believe Beijing to be supportive of the coup.

State-run television confirmed on Monday that a police officer was shot dead in the city of Bago during a protest.

The Yangon court hearing for Suu Kyi -- who spent more than 15 years in house arrest under previous military rule -- is expected to start by video link around 10 am (0330 GMT), her lawyer Khin Maung Zaw told AFP.

The Nobel laureate faces at least four charges: possessing unlicensed walkie-talkies, violating coronavirus restrictions, breaching telecommunications laws and intent to cause public unrest.

Military authorities have also accused her of accepting illegal payments of $600,000 in cash as well as a large quantity of gold -- allegations her lawyer says are "groundless".

"The ruling junta has showed its teeth and taken its mask off... they are showing their true self," Khin Maung Zaw said of Sunday's violence.

Khin Maung Zaw has complained he has not been allowed to meet Suu Kyi, who has been in custody since the coup, though he said the 75-year-old appeared in good health at her last court appearance, by video link, on March 1.

- Chinese factories attacked -

The international community is growing ever more alarmed at the bloodshed, but so far the generals have shown no signs of heeding calls for restraint.

The UN's top rights expert on Myanmar Tom Andrews tweeted that he was "heartbroken/outraged" at Sunday's events.

"Junta leaders don't belong in power, they belong behind bars," he wrote.

"Their supply of cash & weapons must be cut now. I appeal to UN member states to heed my call to act."

On Sunday night state media announced that Yangon's massive Hlaing Tharyar township and the neighbouring Shwepyitha township were being put under martial law.

The move came after protesters and security forces clashed violently and five factories -- several of them Chinese-owned -- in Hlaing Tharyar, a garment-producing district, were razed.

Security forces opened fire on demonstrators wielding sticks and knives, and using cut-out trash cans as shields.

Beijing's embassy in Myanmar issued a statement condemning the actions of "destroyers" and urging police to "guarantee the security" of Chinese businesses.

The declaration of martial law means anyone arrested in the two townships faces trial by military tribunal rather than civilian courts, with sentences ranging from three years' hard labour to execution.

The UN envoy for Myanmar Christine Schraner Burgener strongly condemned Sunday's bloodshed, while the former colonial power Britain said it was "appalled" by the use of force "against innocent people."

Last week Andrews, the UN Special Rapporteur on rights in Myanmar, said there was growing evidence that the junta was engaging in crimes against humanity -- including murder, forced disappearances and torture.

The human rights campaign group Amnesty International has also accused the military of using battlefield weapons on unarmed protestors and carrying out premeditated killings.