The military's ruthless suppression of demonstrations against its February 1 power grab has left 543 civilians dead, including 44 children, according to the Assistance Association for Political Prisoners (AAPP), a local monitoring organisation.

As well as breaking up protests with tear gas, rubber bullets and live rounds, security forces have detained some 2,700 people.

Violence has ramped up in recent weeks, with Save the Children saying the death toll of youngsters had more than doubled in the past 12 days.

"We are shocked that children continue to be among the targets of these fatal attacks, despite repeated calls to protect children from harm," the charity said in a statement.

"It is especially horrifying that several of these children were reportedly killed at home, where they should have been safe from harm."

The authorities have made numerous arrests during night raids on the homes of people suspected of supporting the rallies or the civil disobedience movement that has sprung up aimed at stopping the military from running the country.

Human Rights Watch said the junta had "forcibly disappeared" hundreds of people, refusing to confirm their location or allow access to lawyers.

"The military junta's widespread use of arbitrary arrests and enforced disappearances appears designed to strike fear in the hearts of anti-coup protesters," said HRW's Asia director Brad Adams.

"Concerned governments should demand the release of everyone disappeared and impose targeted economic sanctions against junta leaders to finally hold this abusive military to account."

- 'Rapidly deteriorating situation' -

Outrage from world powers has been growing at the increasing violence, and on Thursday the UN Security Council unanimously "expressed deep concern at the rapidly deteriorating situation", condemning violence against peaceful protesters.

Britain announced a new round of sanctions, this time targeting the junta's extensive business interests, as well as a $700,000 contribution towards UN efforts to document serious human rights violations in Myanmar.

But so far neither sanctions nor calls for restraint have shown any sign of holding back the junta as it struggles to quell the widespread unrest.

There were more protests around the country on Friday, according to local media reports.

In Yangon, people left flowers at bus stops and other public spots in memory of those killed in the crackdown.

The junta has throttled communications in an effort to stop news getting out, and on Thursday it ordered a complete shutdown of wireless internet services.

- Suu Kyi secrets charge -

Ousted civilian leader Aung San Suu Kyi has meanwhile been hit with a new criminal charge, accused of breaking an official secrets law.

The 75-year-old, a democracy icon in Myanmar for decades, faces a raft of charges and conviction would see her barred from political office for the rest of her life.

She appeared in court by video link on Thursday and appeared in good health, according to her legal team, despite two months in detention.

Meanwhile another leading figure in Myanmar's struggle for democracy, Mya Aye, was charged on Thursday under a law against inciting people to commit criminal offences, his lawyer told AFP.

Mya Aye is one of the leaders of the 88 Generation, a veteran pro-democracy group that came of age during an uprising against junta rule in 1988.

That movement was brutally suppressed by the military, with thousands gunned down by soldiers.

The military has defended its coup with claims of fraud in the November election which Suu Kyi's National League for Democracy won by a landslide.

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