South Korean President Moon Jae-in said on Thursday that the wartime sexual slavery issue of “comfort women” cannot be resolved by a 2015 agreement with Japan.

Moon’s comments came a day after Seoul’s Foreign Ministry confirmed a secret deal in the 2015 agreement, Xinhua news agency reported.

The government in Seoul then under impeached President Park Geun-hye made the secret deal with Tokyo-led by Prime Minister Shinzo Abe over South Korean victims, who were forced into sexual servitude for Japanese military brothels during World War II.

Moon said though the deal was inked by leaders of both nations, he, as the president of South Korea, should make it clear again that the comfort women issue could not be resolved by that deal.

Moon said he felt sad when he was briefed on a review report over the 2015 deal, presidential spokesman Park Soo-hyun said.