Japan plans to make public some testimony denying that Koreans were forced to work under harsh conditions during World War II at what is now a UNESCO World Cultural Heritage site, government sources have said.

The controversial move could draw an angry rebuke from Seoul, which maintains that Korean workers were forced to toil in the Hashima Coal Mine off Nagasaki, on what is now known as Gunkanjima ("Battleship Island"), when the Korean Peninsula was under Japanese colonial rule between 1910 and 1945.

When the island was listed as a World Cultural Heritage site in 2015, Tokyo promised Seoul it would exhibit the history of Koreans forced to work there. Japan may continue to collect more testimony, potentially including acknowledgements of forced labor.