One more South Korean victim forced to serve as a sex slave for Japan's Imperial Army during the World War II has passed away, leaving the living victims at 48, an advocacy group for the victims said Monday.

Choi Keum-seon, 90, died of natural cases on Sunday night, the Korean Council for Women Drafted for Military Sexual Slavery by Japan said on its Facebook account. She had been treated at a hospital for her old age.

With her death, the living comfort women victims fell to 48. The comfort women refer to women coerced into sex enslavement at Japanese military brothels during the World War II.

According to historians, at least 200,000 women, mostly Koreans, were deceivably or forcibly mobilized to comfort stations of Japan 's Imperial Army in Japan, China, Southeast Asia and islands of the South Pacific.

Among 238 Korean women who identified themselves as former sex slaves, only 48 are alive as seven died of old age in 2015 alone.

The comfort women victims and civic group activists have held a rally every Wednesday in front of the Japanese embassy in Seoul since Jan. 8, 1992, calling for apology and reparation from the Japanese government.