YANGON — An Australian professor and former adviser to Myanmar's ousted leader Aung San Suu Kyi has been jailed for three years by military authorities.

Sean Turnell was detained in Yangon in February 2021, days after the junta arrested Ms Suu Kyi and overthrew her elected government in a coup.

He was charged along with Ms Suu Kyi for breaching the Official Secrets Act - allegations they've both denied.

Both were sentenced on Thursday in trials criticised by rights groups.

Their trials operated in a closed military court.

"Sean Turnell was denied a fair trial or adequate access to legal counsel and consular assistance. The proceedings have been an outright sham...[and] is the latest in a string of politically motivated cases," said Amnesty International Australia Impact Director Tim O'Connor.

Ms Suu Kyi was sentenced to another three years in jail for breaching the same act. She had already been sentenced to more than two decades in prison on over a dozen counts brought by the military government - with several charges still remaining.

If convicted on all charges, she could face almost 200 years in prison.

At his trial in August, Mr Turnell strongly denied the accusations of violating the nation's state secrets act - which carries a maximum penalty of 14 years in jail.

The Australian economist, based in Myanmar since 2017, had worked as an adviser to the civilian government led by Ms Suu Kyi prior to the coup.

The past year had seen significant international pressure and foreign lobbying for his release.

The Australian government had consistently called on the junta to release him, while Cambodian Prime Minister Hun Sen also appealed for his freedom in a meeting with Myanmar's military leader General Min Aung Hlaing earlier this year.

Mr Turnell was also convicted of breaching an immigration law on Thursday and handed a three-year sentence, for which the court said he would serve concurrently.

Myanmar's military overthrew Aung San Suu Kyi's democratically elected government in February 2021 - sparking huge protests across the country and a widespread resistance movement.

It's estimated more than 15,600 people - including Ms Suu Kyi, other lawmakers, activists and journalists - have been arrested since the military seized power.

More than 12,000 people remain detained while at least 2,322 political prisoners have been killed by the regime says the Assistance Association for Political Prisoners monitoring group.

Earlier this month, Britain's former ambassador to Myanmar Vicky Bowman and her husband were both jailed for a year for breaching immigration laws. Their case is also seen to about wider political concerns than immigration offences, for which foreigners are rarely prosecuted in Myanmar. — BBC