South Korea said Wednesday at least 1,500 Koreans were forced into labor at industrial sites, for which Japan has been pushing to win UNESCO world heritage status.

Japan has sought to win UNESCO's recognition for 23 locales, including mines, shipyards and factories in eight of its prefectures, claiming they have helped lay the groundwork for its modernization that began in 1910.

South Korea's Prime Minister's Office, however, said 1,516 Koreans were forced to carry out dangerous tasks in poor working conditions at these facilities run by four Japanese companies: Mitsubishi Heavy Industries, Mitsubishi Mining, Mitsui Mining and Nippon Steel.

The office came to that number after analyzing damage reports submitted by former forced laborers between 2005 and 2008.

But because the time window is so short, the actual number could be significantly higher, the office said, adding that's why its number may differ from figures suggested by academics and civic organizations in Japan.

"The number could increase exponentially if we allow more people to submit damage reports," an official at the Prime Minister's Office said on condition of anonymity. "The Japanese government should first investigate the extent of damages done to these forced laborers before seeking UNESCO's recognition."

The Japanese government and the employers of these forced laborers have refused to release the exact figure.

According to the office, at least a hundred of them never made their way back to Korea, having died or went missing in Japan. Only 94 of the 1,500 are alive today.

All together, historians estimate that tens of thousands of Koreans were mobilized as slave laborers for Japanese firms during World War II, when Korea was a colony of Japan. (Yonhap)