Japan has submitted a revised version of a recommendation letter to UNESCO as it seeks a World Heritage listing for a mine complex on Sado Island off Niigata Prefecture, a site that is linked to wartime forced labor.

According to NHK, a "tentative" recommendation letter was submitted to UNESCO headquarters in Paris on Thursday with plans to hand in a formal bid around February after consultations with the UN agency.

Japan's first letter submitted in February this year was found insufficient and therefore shot down by UNESCO. The agency did not proceed with its review.

In the revised version, Tokyo has added explanations about severed waterways at the mine, an omitted detail noted by UNESCO.

Over a thousand Koreans are estimated to have been forced to labor at the former gold mine, which later transformed to supply war materials such as copper, iron and zinc during the Pacific War.   

Japan has effectively omitted this part of the mine's history in its UNESCO bid by limiting the time period from the 16th to the mid-19th century.