Danny Fenster, managing editor of Frontier Myanmar, was held in May as he attempted to leave the country.

He is currently on trial for allegedly encouraging dissent against the military and unlawful association, and faces six years in jail if convicted on both counts.

At his latest hearing inside Yangon's Insein prison on Wednesday, "he was told another charge was added" for allegedly breaching immigration law, his lawyer Than Zaw Aung told AFP.

The charge carries a maximum of five years in jail and the trial was expected to begin on Friday, he said.

"We do not know the exact reason for adding (the) immigration charge," he said, adding Fenster's visa was still valid when he was detained.

The new charge comes a day after former US diplomat and hostage negotiator Bill Richardson met junta chief Min Aung Hlaing in the capital Naypyidaw, handing the increasingly isolated junta some rare publicity.

Richardson is in the country on a "private humanitarian mission", his organisation said in a statement announcing the trip that did not mention whether he would seek Fenster's release.

The former governor of New Mexico has negotiated "the release of hostages and American servicemen in North Korea, Cuba, Iraq and the Sudan", according to his centre's website.

Fenster, 37, "is in good health physically but he's upset because of increased charges", Than Zaw Aung said.

He is believed to have contracted Covid-19 during his detention, family members said during a conference call with American journalists in August.

Myanmar has been in turmoil since the military seized power in a February 1 coup and ousted Aung San Suu Kyi's elected government.

More than 1,200 people have been killed by security forces in a crackdown on dissent, according to a local monitoring group.

The press has also been squeezed as the junta tries to tighten control over the flow of information, throttling internet access and revoking the licences of local media outlets.