(CNN) -- Another voice that could have told about the horrors of being a "comfort woman" -- a sex slave used by Japanese soldiers during World War II -- has fallen silent, according to South Korean authorities.

Hwang Keum-ja, 89, died of lung and respiratory disease at a hospital in Seoul Sunday.

Cho Yoon-sun, South Korea's Minister of Gender and Equality and Family, said she had been attempting to meet each of her country's surviving comfort women individually, but had not yet visited Hwang.

"My heart is aching as she died before I was able to meet her," she said in a statement, praising Hwang for her efforts to support others despite the hardships she faced, and vowing that her government would deliver greater support to other comfort women....