Turnell, an Australian economics professor, was working as an advisor to civilian leader Aung San Suu Kyi when he was arrested last February, just days after a military coup.

He has been charged with violating Myanmar's official secrets law and faces a maximum penalty of 14 years in prison if found guilty.

"Professor Turnell's detention is unjust, and we reject the allegations against him," Australian Foreign Minister Marise Payne said in a statement.

"We once again call for Professor Turnell's immediate release."

The coup triggered mass protests and a bloody military crackdown, with more than 1,500 civilians killed and nearly 12,000 arrested as of February 4, according to a local monitoring group.

Human rights groups have raised concerns about Turnell's prosecution, particularly after the Australian embassy was denied access to his court hearing in September.

"Consistent with basic standards of justice and transparency, we expect that Professor Turnell should have unimpeded access to his lawyers, and that Australian officials be able to observe his court proceedings," Payne said.

Turnell was in the middle of a phone interview with the BBC when he was detained after the coup.

"I've just been detained at the moment, and perhaps charged with something, I don't know what that would be, could be anything at all of course," Turnell told the broadcaster at the time.

"Everyone's been very polite and all that, but obviously I'm not free to move or anything like that."

Last month, a coalition of NGOs, including Human Rights Watch and the Refugee Council of Australia, called on the Australian government to impose targeted sanctions on Myanmar's military leaders.