South Korean President Moon Jae-In has stirred up a decades-old dispute with Japan, a move that risks disrupting the international effort to contain North Korea.

For years, Seoul and Tokyo have been at loggerheads over the matter of comfort women — the thousands of girls and women, many of them Korean, who were forced to work in Japan's military brothels during World War II. The two countries reached an agreement in 2015, in which Tokyo shelled out $8.8 million to a fund for victims, but Moon on Thursday criticized that deal, saying it "cannot solve the comfort women issue."

His comments came after a South Korean panel concluded that the 2015 treaty failed to meet victims' demands for compensation. In response to the panel's findings, Japanese Foreign Minister Taro Kono warned that any attempt to revise the agreement "would make Japan's ties with South Korea unmanageable."

The matter is where protesters last week called on the government to nullify the deal, and considered crucial to Moon's populist base.