A South Korean researcher has reportedly identified over 700 Koreans forced to work at a Japanese mine that Tokyo is seeking to register as a UNESCO global cultural heritage.

Jung Hye-kyung, a leading researcher of a civic group focused on Japan’s wartime forced labor, told Yonhap News on Monday that she has verified the names of 745 Korean workers at the Sado mine based on three lists regarding cigarette rations at the site and other documents.

The finding, also published recently in the Journal of Korean-Japanese National Studies, involves the full names of some 580 Koreans, while the other 160 were identified through parts of their names or their Japanese names.

Although a brief history published by the Sado mine operators acknowledges the presence of over 15-hundred Koreans at the mine in 1945, efforts to assess the scope of Japan’s forced labor at the site have been limited due to difficulty identifying the victims. So far, only about 150 have been reported to the South Korean government.

The Japanese government has worked for years to secure UNESCO World Heritage Site recognition for the gold mine located on Sado Island in Niigata Prefecture northwest of Tokyo.