Danny Fenster, who was arrested as he tried to leave the country in May, was hit with "two charges under section 50(a) of the Counter Terrorism Law and 124(a) of the Penal Code," his lawyer Than Zaw Aung told AFP.

Conviction under the counter-terrorism law carries a maximum sentence of life imprisonment.

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

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.

Fenster 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.