South Korea's president has criticized Japan's insistence that the issue of women forced to provide sex for Japanese troops in World War II has been settled.

President Moon Jae-in said Thursday that Japan "should not say the matter is closed." He added that "a crime against humanity committed in time of war cannot be closed with just a word."

So-called comfort women provided sex for Japan's military in conditions that many experts say were sexual slavery. Many of the women were from Korea, then a colony of Japan, who were taken to front-line brothels.

The previous South Korean government signed an accord with Japan in late 2015 to settle the issue, which has bedeviled bilateral relations. The Japanese government said it lodged a "strong protest" over Moon's remarks.