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

South Korea’s foreign ministry did 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, Yonhap news agency reported.

The decision was seen as stoking doubt over Japan’s sincerity in honouring 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 South 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.

Of the approximately 100 planned attendees, around 30 seats were left vacant due to the boycott of the Korean delegation.

During the ceremony, Ikuina delivered a speech notably omitting any mention of “forced labour” and exited the venue without responding to reporters’ questions.

Sado City Mayor Ryugo Watanabe described the boycott by the Korean side as “regrettable.”

Nine of the eleven family members of the Korean victims are already in Japan, and they are set to hold a separate event at 9 a.m. on Monday honouring the victims at a site near the mine complex that used to be a dormitory for Koreans.

The memorial ceremony, which will be attended by South Korea’s top envoy in Japan, is expected to comprise an address honouring the victims and a silent tribute, followed by laying wreaths for the victims.

South Korea’s foreign ministry said Sunday that holding a separate ceremony honouring the forced labour victims reflects the government’s “firm resolve not to compromise on historical issues with Japan.”

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 South 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 honour 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.