Choi Jang-seob was 13 years old when he was drafted to work in a coal mine in Japan toward the end of World War II.

Sent by train and boat from his native South Korea, Mr. Choi, now 86, joined other boys to fill holes in mine shafts on the island of Hashima to prevent them from collapsing. Still, cave-ins and other accidents killed a few workers each month in the hot and humid tunnels, he said.

The island where Mr. Choi toiled is one of the latest sources of tension between South Korea and Japan over war history, 70 years after Tokyo’s World War II surrender ended its occupation of the Korean peninsula. Japan is pressing for Hashima and 22 other landmarks of its industrialization to be added to a list of global landmarks certified by the United Nations for their cultural or historical significance.