A Myanmar junta court sentenced the country's ousted leader Aung San Suu Kyi to a further three years in prison Thursday while also jailing an Australian economist, a source with knowledge of the case told AFP.

Detained since the putsch last year, Suu Kyi has already been convicted of corruption and a clutch of other charges by a closed court.

She and Sean Turnell received a three-year sentence under the state secrets act on Thursday.

Both had been detained since a coup in February last year in which the military ousted Suu Kyi's government, for which Turnell was an adviser.

"Mr Sean Turnell, Daw Aung San Suu Kyi and another three were sentenced to three years imprisonment each under State Secret Act," the source told AFP, adding that Suu Kyi would appeal her verdict.

The source added that a separate case against Turnell, under the country's immigration act, was ongoing.

His arrest last year prompted outrage, with Australian diplomats lobbying Myanmar's regional neighbors to assist with the case.

The 76-year-old was in the middle of a phone interview with the BBC when he was detained after the 2021 coup.

"I've just been detained at the moment, and perhaps charged with something, I don't know what that would be, could be anything at all of course," Turnell told the broadcaster at the time.

In August of this year he pleaded not guilty to breaching the colonial-era official secrets act during his trial in a secretive junta court — inaccessible to journalists — in the capital Naypyidaw.

The exact details of Turnell's alleged offence have not been made public, though state television has said he had access to "secret state financial information" and had tried to flee the country.

Myanmar has been in turmoil since the military seized power last year and ousted Suu Kyi's elected government.

Since the putsch last year, more than 2,200 people have been killed and 15,000 arrested in a military crackdown on dissent, according to a local monitoring group.