Since it seized power more than two years ago and plunged the country into turmoil, the junta has arrested tens of thousands in a sweeping and bloody crackdown on dissent.

Rights groups say the military has used the courts to throttle opponents including democracy figurehead Aung San Suu Kyi and former president Win Myint, who were jailed for lengthy terms by closed-door courts.

Defence lawyers working in "special courts" set up by the junta to try political crimes face harassment, intimidation and threats from authorities, HRW said in a report based on interviews with 19 lawyers.

"In the courtroom, I now have to worry about not getting myself detained rather than speaking the truth," one Yangon-based lawyer told the watchdog.

"Everyone at the court knows who I am... The junta can detain me at any time, and they can and will make up any reasons they want."

HRW cited the case of attorney Ywet Nu Aung, who was reportedly detained as she left a hearing where she was representing a former chief minister and member of Suu Kyi's party, the National League for Democracy (NLD).

She was accused of helping to provide financial support to anti-junta militias and later sentenced to 15 years in prison with hard labour.

Lawyers are regularly barred from communicating privately with clients ahead of hearings, HRW said, and in an overcrowded legal system, some had taken on hundreds of cases.

"Sometimes cross-examination doesn't even happen," another lawyer told HRW.

"It's near impossible to challenge what they (the prosecution) present as evidence, and we never get to have a defendant released on bail."

All 19 lawyers told HRW they had experienced "intimidation and surveillance by junta authorities".

"Few have been willing to put themselves at risk of further surveillance and intimidation and many have stopped taking cases," HRW said.

More than 23,000 people have been arrested by the junta since the coup in February 2021, according to a local monitoring group.

Last year, a junta-controlled court ordered the execution of a former NLD lawmaker along with a prominent activist over allegations of "terrorism" -- Myanmar's first use of capital punishment in decades.