South Korea on Sunday dug its heels ahead of talks with Japan over the thorny issue of wartime sex slaves that has long strained ties.

Foreign Minister Yun Byung-se dismissed Japan's claim that the issue of "comfort women" who were forced to work in Japanese military brothels during World War II was settled in a 1965 agreement on normalizing relations.

"There is no change to our position and there won't be any in the future," Yun told journalists as senior officials of the two countries met to prepare for talks between Yun and his counterpart Fumio Kishida on Monday.

Japan has long maintained that the dispute was settled in 1965, when Tokyo made a total payment of $800 million in grants or loans to its former colony.

But Seoul says the treaty does not cover compensation for victims of wartime wrongdoing, such as the comfort women, and that the agreement does not absolve the Japanese government of its legal responsibility.

South Korean President Park Geun-hye has said settlement of the issue remains the "greatest stumbling block" to friendlier ties. When she met Japanese Prime Minister Shinzo Abe in Seoul last month, they agreed to speed up talks on the issue. The foreign ministers' meeting on Monday is part of such efforts.

Up to 200,000 women are estimated to have been sexually enslaved by Japan during the war, many of them Korean. Seoul is demanding a formal apology and compensation for the 46 surviving Korean "comfort women".

Japan issued a landmark 1993 statement that expressed "sincere apologies and remorse" to the women "who suffered immeasurable pain and incurable physical and psychological wounds as comfort women".

Abe, who once added fuel to the row by questioning whether comfort women were really "forced" against their will to serve Japanese soldiers, says his government stands by the 1993 statement.

In a fresh irritant ahead of the foreign ministers' talks, Japanese news reports said Seoul was reviewing the relocation of a statue symbolizing the comfort women at the request of Tokyo. The statue currently stands in front of the Japanese embassy in Seoul.