Suu Kyi, 77, has been detained since the generals toppled her government in a coup on February 1 last year, ending the Southeast Asian country’s brief period of democracy.
She has since been hit with a series of charges, including violating the official secrets act, corruption and electoral fraud. She faces decades in jail if convicted on all counts.
Suu Kyi was sentenced to “six years imprisonment under four anti-corruption charges”, said the source, who requested anonymity because they are not authorised to speak to the media.
She appeared in good health and did not make any statement following her latest sentencing, the source added.
A junta spokesman could not be reached for comment.
The Nobel laureate has already been sentenced to 11 years in jail for corruption, incitement against the military, breaching Covid-19 rules and breaking a telecommunications law.
Journalists have been barred from attending the court hearings and Suu Kyi’s lawyers have been banned from speaking to the media.
The coup sparked widespread protests and unrest, and renewed fighting with established ethnic rebel groups.
Dozens of “People’s Defence Forces” have also sprung up to fight the junta and have surprised the military with their effectiveness, analysts say.
According to a local monitoring group, the crackdown has left more than 2,000 civilians dead and seen some 17,000 arrested.
– ‘Erase the past’ –
Suu Kyi has been the face of Myanmar’s democratic hopes for more than 30 years, but her earlier six-year sentence already meant she is likely to miss elections the junta says it plans to hold by next year.
“Immune from domestic and international outrage, the punishment trials against Suu Kyi and her supporters are designed to erase the democratic past,” independent Myanmar analyst David Mathieson told AFP.
“Their intent is clear to everyone it seems, everyone but the international community.”
In June, Suu Kyi was transferred from house arrest to a prison in the capital Naypyidaw, where her trial continues in a courthouse inside the prison compound.
She remains confined to the jail, with her link to the outside world limited to brief pre-trial meetings with lawyers.
Many of her political allies have also been arrested since the coup, with one chief minister sentenced to 75 years in jail.
Last month, the junta stoked renewed international condemnation when it executed Phyo Zeya Thaw, a former lawmaker from her National League for Democracy (NLD) party for offences under anti-terrorism laws.
Suu Kyi learned of the execution at a pre-trial hearing, a source with knowledge of the matter said, but has yet to speak on the matter.