Sean Turnell was working as an adviser to Myanmar civilian leader Aung San Suu Kyi when he was detained shortly after the coup in February last year.

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

On Monday morning, Hun Sen said Turnell had "been released" the previous day but by the evening he issued a retraction on Facebook saying he had "received the wrong information".

"I would like to ask for understanding for this unintentional mistake," he said in the Facebook post.

The Cambodian strongman, who met with Myanmar's junta chief last month, said earlier on Monday that he had passed on a request from the Australian government for Turnell's release.

Hun Sen said Min Aung Hlaing responded that he "would consider it positively".

Junta spokesman Zaw Min Tun denied that Turnell had been released, but acknowledged that Hun Sen had brought up the matter during his visit -- the first to Myanmar by any foreign leader since last year's coup.

"Regarding this matter, Senior General Min Aung Hlaing said he would think about it after his legal case is finished," he told AFP.

Turnell has appeared in court every Thursday in the capital Naypyidaw for his trial -- where he is co-accused alongside Suu Kyi.

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

The exact details of Turnell's alleged offence have not been made public, although state television has said he had access to "secret state financial information" and tried to flee the country.

Australia's Department of Foreign Affairs and Trade on Monday renewed its call for Turnell's "immediate release and for his rights and welfare to be upheld".