SADO, Japan — Japan held a memorial service on Sunday near the Sado Island Gold Mines, despite South Korea's last-minute boycott of the event 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.