Myanmar's detained former leader Aung San Suu Kyi has been given a further one-sixth reduction in her sentence as part of an amnesty, a member of her legal team says, the second such commutation in two weeks.

The Nobel laureate, who has been held since being toppled by the military in a 2021 coup, would now have just more than 18 years left to serve, the legal team member said, declining to be identified by name.

After a marathon run of trials, Aung San Suu Kyi, 80, was sentenced to 33 years after convictions on charges ranging from corruption and inciting election fraud to violating state secrecy rules, which her allies maintain were politically motivated and aimed at sidelining her.

That sentence was was later commuted to 27 years, and then by a sixth in a Myanmar New Year amnesty on April 17 that freed her ally and co-defendant Win Myint, the former president.

The latest reduction comes after an announcement by state media on Thursday saying that all prisoners would have their sentences commuted.

Aung San Suu Kyi's whereabouts are unknown and she has not been seen in public since the trials.

Authorities continue to hold her at an undisclosed location, and the government has yet to grant her legal team or family face-to-face access.

A spokesperson for the military-backed government did not immediately respond to calls seeking comment.

Myanmar's new President Min Aung Hlaing, who overthrew Aung San Suu Kyi in the coup, has faced persistent international pressure to release political detainees since a recent election, including from the Southeast Asian bloc ASEAN, which he is seeking to re-engage with after being barred from its summits.

Min Aung Hlaing last week told Thailand's foreign minister she was being "well looked after" and his government was considering unspecified "good things".