US Secretary of State Antony Blinken on Thursday welcomed Myanmar's release of thousands of prisoners, including a US citizen and other foreigners, but said there was no sign the junta was opening up.

"It is one bright spot in what is otherwise an incredibly dark time, where we see things going from bad to worse in Burma," Blinken said, using Myanmar's former name.

"While we are pleased to see the release of those wrongfully detained, I can't tell you that it suggests anything larger about whether there is a genuine change in direction by the regime," he told reporters at an Asia-Pacific summit in Bangkok.

Blinken said that the freed prisoners included Kyaw Htay Oo, a naturalised US citizen who was arrested more than a year ago following the military's takeover.

The US ambassador in Myanmar, Thomas Vajda, saw him before he flew out on Thursday, Blinken said.

Blinken said that despite the release of prisoners, the regime was also responsible for "terrible violence" as he pointed to an air attack that killed children at a school and executions of activists.

He said there was also no sign that the military leadership has moved forward on a compromise plan put forward by the Association of Southeast Asian Nations.

"What we will be looking for is actions over the days, the weeks and the months ahead and that is how we will judge whether this represents any kind of change or not," Blinken said.

AFP