A Myanmar junta court sentenced ousted leader Aung San Suu Kyi to three years in jail on Friday for electoral fraud over 2020 polls which her party won in a landslide.

Suu Kyi was "sentenced to three years' imprisonment with hard labour", a source with knowledge of the case said, adding that the Nobel laureate, 77, appeared to be in good health.

Detained since a putsch last year, Suu Kyi has already been convicted of corruption and a clutch of other charges by a closed junta court and sentenced to 17 years in prison.

Journalists have been barred from proceedings in the military-built capital Naypyidaw and her lawyers have been prevented from speaking to the press.

The military alleged widespread voter fraud during the November 2020 election, won resoundingly by Suu Kyi's National League for Democracy (NLD), although international observers said the poll was largely free and fair.

The military has since cancelled the result and said it uncovered more than 11 million instances of voter fraud.

Last month junta chief Min Aung Hlaing said the military was being "lenient" on Suu Kyi and could have taken "more serious actions" against her.

Myanmar was plunged into crisis following the military's power grab last year, with swathes of the country ravaged by fighting and the economy in freefall.

More than 2,200 people have been killed and over 15,000 arrested in the military's crackdown on dissent since it seized power, according to a local monitoring group.

The junta declared a state of emergency after ousting Suu Kyi's government, and has previously said elections would be held and the state of emergency lifted by August 2023.

In a speech broadcast last month Min Aung Hlaing did not mention a date for fresh polls but said they could only be held when the country was "peaceful and stable".

He also said "reform" to the electoral system was needed, including combining the first-past-the-post system -- under which Suu Kyi's NLD has won sweeping majorities -- with proportional representation.

Last month the junta-stacked Union Election Commission said the country's 92 registered political parties would have to ask for permission if they wished to meet foreign organisations or individuals.

"Political parties need to respect the law," the commission said.

"If they fail to do so their party's registration will be dissolved."