Myanmar's military said on Thursday it will release almost 6,000 prisoners, including a former British ambassador, a Japanese journalist and an Australian economics adviser in a rare olive branch from the isolated junta.

The Southeast Asian country has been in turmoil since the military's coup last year and a bloody crackdown on dissent that has seen thousands jailed.

Dozens of foreign nationals have been caught up in the crackdown.

Former British envoy Vicky Bowman, Australian economics adviser Sean Turnell and Japanese journalist Toru Kubota "will be released to mark National Day", a senior officer said.

"Altogether, 5,774 prisoners including some 600 women prisoners will be released," they said, revising an earlier figure of about 700.

They did not say how many of those pardoned had been arrested during the military's crackdown on dissent.

Bowman, who served as ambassador from 2002 to 2006, was detained with her husband in August for failing to declare she was living at an address different from the one listed on her foreigner's registration certificate.

They were later jailed for one year. Her husband, prominent artist Htein Lin, will also be released, the official said.

Sean Turnell was working as an adviser to Myanmar's civilian leader Suu Kyi when he was detained shortly after the coup in February last year.

In September, he and Suu Kyi were convicted by a closed junta court of breaching the official secrets act and jailed for three years each.

Kubota, 26, was detained in July near an anti-government rally in Yangon along with two Myanmar citizens and jailed for 10 years.

A source at Japan's embassy in Myanmar said they had "been informed that Mr Kubota will be released today" by junta authorities.

Kubota would leave for Japan "today", they added.

Kubota is the fifth foreign journalist to be detained in Myanmar, after US citizens Nathan Maung and Danny Fenster, Robert Bociaga of Poland and Yuki Kitazumi of Japan – all of whom were later freed and deported. (AFP)