The military has squeezed the press since taking power in a February coup, arresting dozens of journalists critical of its crackdown on dissent that has killed over 1,200 people, according to a local monitoring group.

Danny Fenster, who had been working for local outlet Frontier Myanmar for around a year, was arrested as he was heading home to see his family in May and has been held in Yangon's Insein prison since.

The 37-year-old is already on trial for allegedly encouraging dissent against the military, unlawful association and breaching immigration law.

The additional charges under Myanmar's anti-terror and sedition laws open Fenster up to a maximum sentence of life imprisonment. The trial is scheduled to begin on November 16.

"He has become quite thin," Than Zaw Aung said.

Fenster was "disappointed" at being hit with the new charges, which were filed on Tuesday, the lawyer added.

They come days 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 has previously negotiated the release of prisoners and US servicemen in North Korea, Cuba, Iraq and Sudan and has recently sought to free US-affiliated inmates in Venezuela.

The former UN ambassador said he was hopeful he had brokered a deal for a resumption of visits by the International Committee of the Red Cross to prisons -- which have been filled with political prisoners.

Richardson, declining to give further details, said the US State Department asked him not to raise Fenster's case during his visit.

"Danny's case has become emblematic of the utter contempt Myanmar's military has for independent media," Emerlynne Gil, Amnesty International's deputy regional director for research, said in a statement.

"These harsh new charges only further highlight the clumsy attempt to prosecute an independent journalist who should be freed immediately and unconditionally so he can be reunited with his family and friends."

- Press clampdown -

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

He last spoke with US consular officials by phone on October 31, State Department spokesman Ned Price said Monday, adding Washington remained "deeply concerned over his continued detention".

The Southeast Asian country has been mired in chaos since the military ousted Aung San Suu Kyi's elected government, with the junta trying to crush widespread democracy protests and stamp out dissent.

The military has tightened control over the flow of information, throttling internet access and revoking the licences of local media outlets.

Several journalists critical of the military government were among those released last month in a junta amnesty to mark a Buddhist festival.

More than 100 journalists have been arrested since the putsch, according to Reporting ASEAN, a monitoring group.

It says 31 are still in detention.

The coup snuffed out the country's short-lived experiment with democracy, with civilian leader Suu Kyi now facing a raft of charges in a junta court that could see her jailed for decades.