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.

The United States on Wednesday urged Myanmar's junta to immediately free Fenster.

"The profoundly unjust nature of Danny's detention is plain for all the world to see, a State Department spokesperson told AFP.

"The regime should take the prudent step of releasing him now... His continued detention is unacceptable. Journalism is not a crime."

The new charges 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.

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.

- Press clampdown -

The Southeast Asian country has been mired in chaos since the military ousted the 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 an 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 Aung San Suu Kyi now facing a raft of charges that could see her jailed for decades.