SEOUL -- South Korea on Wednesday confirmed the existence of secret agreement with Japan in the 2015 deal between the two countries over the sexual slavery victims of South Korea who were forced into sex enslavement for Japanese military brothels during World War II.

The task force team under Seoul's foreign ministry announced a review result on the deal with Japan, reached on Dec 28, 2015 under the previous South Korean government to reach a "final and irreversible" agreement on comfort women victims.

Comfort women refers to the Korean women who were kidnapped, coerced or duped into sex servitude for Japan's Imperial Army during the Pacific War. Historians say up to 200,000 girls and young women fell victim to the war crime against humanity.

The review result said some of the bilateral agreements was not disclosed to the general public, noting that Japan demanded South Korea persuade civic groups supporting the sex slavery victims to accept the 2015 deal.

Then South Korean government under impeached President Park Geun-hye promised to make efforts at persuading the advocacy groups for the victims, actually accepting the Japanese side's demand, the task force team said.

The South Korean victims harshly protested against the deal after foreign ministers of the two countries announced it. Under the deal, Japan vowed to provide 1 billion yen (about 9 million US dollars) for a foundation dedicated to supporting the sex slavery victims in return for South Korea's final and irreversible agreement to the wartime atrocity.

The victims said the Japanese government had yet to take its legal responsibility and make its sincere apology for the wartime brutality, demanding the annulment of the 2015 deal.

The new South Korean government under President Moon Jae-in who took office in May, said the 2015 deal was not "emotionally" acceptable to ordinary South Koreans, ordering a review of the whole procedure in reaching the agreement.