A top US official has held a virtual meeting with two representatives of Myanmar’s National Unity Government (NUG), an administration set up by opponents of the February 1 military coup that plunged the country into chaos.

National Security Adviser Jake Sullivan met Duwa Lashi La and Zin Mar Aung from the NUG in a virtual meeting on Monday, the White House said in a statement.

Sullivan stressed "continued US support for the pro-democracy movement” in Myanmar and discussed ongoing efforts to restore democracy in the wake of the military’s power grab. He also expressed concern "over the military’s brutal violence” and said the US would "continue to promote accountability for the coup”.

More than 1,000 people have been killed since the armed forces under Senior General Min Aung Hlaing seized power from the elected government of Aung San Suu Kyi and her National League for Democracy party nine months ago. Aung San Suu Kyi has been detained ever since and faces multiple court cases that could put her behind bars for years.

Thousands have also been arrested for opposing military rule, according to the Assistance Association of Political Prisoners which has been tracking the post-coup crackdown.

Kyaw Min Yu, better known as Ko Jimmy, who rose to prominence during Myanmar’s 1988 student uprising, was the latest to be arrested after he was detained in an overnight raid on Sunday.

Sullivan said the US would continue to call for his release and everyone who had been "unjustly detained”.

There was also discussion on regional and international engagement, with the Association of Southeast Asian Nations beginning its annual summit on Tuesday.

The 10-member group has barred Min Aung Hlaing from attending because of the military’s lack of commitment to a consensus agreed in April under which it was supposed to end violence, and allow a special envoy to visit and discuss the political situation with all parties.

Sullivan stressed support for ASEAN efforts to hold the military regime to its obligations.