Japan is believed to have recommended the controversial Sado mine for a UNESCO World Heritage designation without mentioning its history as a site of forced labor for Korean laborers.

A Japanese government official told Seoul-based Yonhap News Agency on Monday that, in recommending the mine, Tokyo noted that the mine’s manufacturing technique and production system between the 16th and mid-19th century justify a World Heritage site designation.

Tokyo has not revealed precisely the time period mentioned in the recommendation submitted on February 1. However, the official’s remark appeared to imply that Japan’s colonial rule of Korea between 1910 and 1945 was not noted in the proposal.

When asked by Yonhap if the recommendation or any related material mentioned that Koreans had worked in the mine, the official declined to comment, saying that the recommendation is not open to the public.

Japan had made similar attempts to ignore forced labor charges when it sought to secure UNESCO World Heritage status for 23 Meiji era industrial sites, seven of which were venues of Korean forced labor, including the Hashima Island coal mine and Nagasaki Shipyard. These sites were listed as World Heritage sites in 2015.

Last year, the UNESCO World Heritage Committee expressed regret that information Japan provided on the history of forced labor at the sites was insufficient and asked the country to address the problem.