Visitors walk though a tunnel at Sado Kinzan Gold Mine historic site in Sado, Niigata prefecture, Japan, Nov. 23. AP-Yonhap

A memorial ceremony honoring forced labor victims, including Koreans, at an old Japanese mine complex kicked off as planned Sunday, with Korea boycotting it over Tokyo's pick to send a senior official with hard-line views on history to the event.

Korea's foreign ministry has said it will not attend the memorial ceremony, in response to Tokyo's decision to send Akiko Ikuina, a parliamentary vice minister at Japan's foreign ministry, as the government representative to attend the ceremony.

The decision was seen as stoking doubt over Japan's sincerity in honoring the victims given that Ikuina has visited the Yasukuni Shrine, regarded as a symbol of Japan's militaristic past, and has been a source of tension, with Korea strongly opposing visits or offerings made by Japanese government officials.

A committee overseeing the ceremony pushed ahead with the memorial at 1 p.m. on Japan's Sado Island in Niigata Prefecture, attended by Ikuina, as well as regional and civic group officials, including the governor and mayor of Niigata and Sado.

Visitors look at display at Sado Kinzan Gold Mine historic site in Sado, Niigata prefecture, Japan, Nov. 23. AP-Yonhap

Nine of the eleven family members of the Korean victims are already in Japan, and they are expected to hold a separate memorial and pay visits to sites related to the Sado mines, accompanied by Seoul officials.

Japan has promised to host a memorial event as a condition for Seoul's consent to the location's designation as a UNESCO World Heritage Site, with Sunday's memorial marking the first such event.

More than 1,500 Koreans are estimated to have been forced to toil at the Sado gold and silver mines during World War II, when Korea was under Japan's 1910-45 colonial rule.

Seoul has stressed to Tokyo the importance of holding the ceremony to honor the victims in a sincere manner, requesting the attendance of a high-level official, possibly at a vice minister level.

However, the lack of details about the ceremony's arrangements, even in the days leading up to the event, has sparked speculation in Seoul that negotiations with Tokyo may not have gone smoothly.

The Japanese government on Sunday expressed regret over Korea's decision not to attend the ceremony in response to a question by Yonhap News Agency.

The Japanese Embassy said Seoul and Tokyo had been in "polite communication" over the memorial event, but it "would be regrettable" if Korea does not attend the memorial service.

The latest development adds to concerns that trilateral security cooperation between the two nations, also involving the United States, which had been a catalyst in strengthening bilateral ties between Seoul and Tokyo, could dampen with U.S. President-elect Donald Trump's win.

"Korea-Japan ties could advance on the back of Korea's efforts," said Choi Eun-mi, a research fellow at the Asan Institute for Policy Studies. "Japan should have reacted in a corresponding manner, but unfortunately it didn't happen." (Yonhap)