Myanmar has been in turmoil since civilian leader Aung San Suu Kyi was ousted on February 1, with security forces killing more than 600 people as protesters refuse to submit to military rule.

State media reported Friday that 19 people had been sentenced to death for robbery and murder by a military court, with 17 of them tried in absentia.

They were arrested in Yangon's North Okkalapa township -- one of six areas in the commercial hub currently under martial law, meaning anybody arrested there is tried by a military tribunal.

The six townships are home to about two million people -- more than a quarter of Yangon's sprawling population.

While Myanmar has long had the death penalty in its penal code, the country has not carried out an execution in over 30 years, said Phil Robertson, deputy director of the Asia division for Human Rights Watch.

"It indicates the military are prepared to go back to a time when Myanmar was executing people," he said.

Trying cases in a military court means there can be no appeals, and there are "no guarantees of a free and fair trial in any way, shape or form", he added.

The sentences could be a tactic to force protesters off the streets and back to work, he said, as a nationwide boycott has brought much of Myanmar's economy to a halt.

"Their core mission is to use force and violence to get everybody off the streets and to break apart the (civil disobedience movement)," Robertson said.

Norway also reacted to the death sentences on Saturday, calling them "unacceptable and a deeply worrying development".

"Norway strongly urges Myanmar not to carry out the executions, to stop the violence and allow the UN Special Envoy to visit," said Norwegian foreign minister Ine Eriksen Soreide in a tweet.

United Nations officials say the special envoy, Christine Schraner Burgener, is in neighbouring Thailand hoping to enter Myanmar for face-to-face meetings with the generals to negotiate a path out of the crisis.

The junta has so far refused her entry.

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