Suu Kyi has been in military custody since a coup ousted her government in February last year. (AFP)

Ousted leader Aung San Suu Kyi was sentenced by Myanmar's junta on Wednesday to another six years in prison for corruption, a source revealed, taking her total jail time to 26 years.

Suu Kyi "was sentenced to three years imprisonment each for two corruption cases," in which she had been accused of taking bribes from a businessman, the source said, adding that the terms would be served concurrently.

Suu Kyi has been detained since the coup last year and has already been convicted of corruption and a slew of other offenses by a secret junta court.

In the most recent allegation, she was accused of accepting $550,000 in bribes from businessman Maung Weik.

Suu Kyi appeared in good health and would appeal, the source added.

Journalists are not permitted to attend court proceedings, and Suu Kyi's lawyers are not permitted to speak to the media.

According to a local monitoring group, the military has killed over 2,300 people and imprisoned over 15,000 in its crackdown on dissent since gaining power.

Earlier on August 15, a Myanmar junta court jailed Aung San Suu Kyi for another six years for corruption, a source close to the case said, taking the ousted leader's prison time to 17 years.

She was hit then with a series of charges, including violating the official secrets act, corruption, and electoral fraud.

In addition to the 17 years, she was sentenced to three more years on September 2, adding her sentence to 23 years.

Suu Kyi convicted of corruption

According to a person acquainted with the situation, a Myanmar military court found former Myanmar State Counselor Aung San Suu Kyi guilty of corruption and sentenced her to five years in jail on April 27 this year.

Suu Kyi has faced a torrent of criminal charges since a military coup toppled her administration in February last year, throwing the country into instability.

Some members of the "opposition" government led by Aung San Suu Kyi's toppled administration had their citizenship revoked, Myanmar's junta announced in March.

Ousted politicians created the so-called National Unity Government weeks after the military took power last year, vowing to overthrow it.

Suu Kyi, nominated to lead the organization, has been arrested since the coup and is facing allegations that could land her in prison for more than 150 years.