SADO, Japan, Nov 24, (AP): Japan held a memorial ceremony on Sunday near the Sado Island Gold Mines despite a last-minute boycott of the event by South Korea that highlighted tensions between the neighbors over the issue of Korean forced laborers at the site before and during World War II. South Korea’s absence at Sunday’s memorial, to which Seoul government officials and Korean victims’ families were invited, is a major setback in the rapidly improving ties between the two countries, which since last year have set aside their historical disputes to prioritize US-led security cooperation.

The Sado mines were listed in July as a UNESCO World Heritage site after Japan moved past years of disputes with South Korea and reluctantly acknowledged the mines’ dark history, promising to hold an annual memorial service for all victims, including hundreds of Koreans who were mobilized to work in the mines.

On Saturday, South Korea announced it would not attend the event, saying it was impossible to settle unspecified disagreements between the two governments in time. Families of Korean victims of the mine accidents were expected to separately hold their own ceremony near the mine at a later date. Masashi Mizobuchi, an assistant press secretary in Japan’s Foreign Ministry, said Japan has been in communication with Seoul and called the South Korean decision "disappointing.”

The ceremony was held as planned on Sunday at a facility near the mines, where more than 20 seats for Korean attendees remained vacant. The 16th-century mines on the island of Sado, off Japan’s north-central coast, operated for nearly 400 years before closing in 1989 and were once the world’s largest gold producer.

Historians say about 1,500 Koreans were mobilized to Sado as part of Japan’s use of hundreds of thousands of Korean laborers, including those forcibly brought from the Korean Peninsula, at Japanese mines and factories to make up for labor shortages because most working-age Japanese men had been sent to battlefronts across Asia and the Pacific. Japan’s government has maintained that all wartime compensation issues between the two countries were resolved under a 1965 normalization treaty.