The documents, which will be handed over to Japan next year, were expected to reveal details of prisoners of war taken to camps after the war ended, according to the health, labour and welfare ministry.

Some 575,000 Japanese soldiers and others were taken to Soviet labour camps in Siberia and Mongolia after the war.

Most eventually returned home, but roughly 53,000 people were believed to have died in the camps with the fate of about 18,000 others unknown.

“By analysing the data, the records may shed light on who died where and how,” a ministry official said.

“It may say something about those who died while being transported between labour camps. This kind of data has never been made available before.”