The country has been in turmoil since last year's coup, with mass protests and a subsequent military crackdown that has killed more than 1,500 civilians, according to the UN's human rights office.

Junta chief Min Aung Hlaing issued the "pardon order" -- a regular feature of major holidays in the country -- for 814 prisoners to commemorate Union Day's 75th anniversary, state media said.

Those given amnesty will be mostly from prisons in commercial hub Yangon, junta spokesperson Zaw Min Tun told AFP.

He did not say whether detained Australian academic Sean Turnell -- who has been detained for more than a year -- would be among those released.

Turnell, an Australian economics professor, was working as an adviser to ousted civilian leader Aung San Suu Kyi when he was arrested last February, just days after a military coup.

He has been charged with violating Myanmar's official secrets law and faces a maximum penalty of 14 years in prison if found guilty.

The junta released about 23,000 prisoners last April, with some rights groups at the time fearing the move was to free up space for opponents of the military and cause chaos.

A similar number were released on last year's Union Day as well.

- 'Performance art' -

On Saturday, the junta marked Union Day with a show of force in the military-built capital Naypyidaw, known for its broad and often empty thoroughfares.

Hundreds of troops paraded alongside civil servants waving national flags in unison and troupes performed choreographed dances.

Helicopters carrying the country's yellow, green and red flag flew overhead, followed by jets trailing the same colours in smoke.

Independent Myanmar analyst David Mathieson characterised the parade as "performance art".

"The message for Union Day is at complete odds with the reality that is Myanmar," he told AFP, adding the junta was not sincere about peace.

"It's pretty absurd that on the 75th anniversary of Union Day the country is more divided than at any point in its history."

In a speech to troops, Min Aung Hlaing repeated the military's claim of massive fraud in 2020 elections won by Suu Kyi's party.

He also invited the myriad ethnic armed organisations that have been fighting Myanmar's military -- and each other -- for decades to sit for peace talks.

In an announcement carried by state media, he said the junta would also halt ongoing "criminal proceedings" against members of Rakhine state's Arakan Army, which for years has fought a war for autonomy for the ethnic Rakhine population.

Struggling to contain the backlash and contending with daily clashes, swathes of the country are under the control of anti-coup fighters.

An anti-junta group told local media it was behind an explosion in Naypyidaw hours before Union Day celebrations were due to start. AFP was unable to confirm the reports.