South Korea and Japan held talks on Tokyo's sexual enslavement of Korean women during World War II on Monday, one of the most knotty issues for bilateral ties, Seoul's foreign ministry said.

Lee Sang-deok, Seoul's chief delegate to the talks, met with his Japanese counterpart, Junichi Ihara, in Tokyo in their sixth round of talks to discuss the issue of "comfort women," according to the foreign ministry.

In April, the two historical rivals launched the talks on the sex slavery, but no major progress has been made as Japan has been reluctant to sincerely apologize for the issue.

The meeting came as the two countries are seeking to improve their strained ties as this year marks the 50th anniversary of the normalization of their bilateral relations. The new year also marks the 70th anniversary of Seoul's liberation from Tokyo's colonial rule in 1945.

Since taking office in early 2013, South Korean President Park Geun-hye has shunned a summit with Japanese Prime Minister Shinzo Abe as a show of anger against Tokyo's refusal to atone for its historical wrongdoings.

In her new year press conference on Jan. 12, Park repeatedly urged Japan to face up to history, warning that the issue could be a "big burden" on Japan unless it is quickly resolved.

South Korean Foreign Minister Yun Byung-se told reporters in Seoul earlier in the day that Japan is seen as not offering sufficient conditions for the bilateral summit to be held.

"Japan seems to deal with the sex slavery issue solely from the perspective of a bilateral matter. But the comfort women issue is a matter of universal human rights," Yun said.

The foreign minister expressed hope that the Seoul-Tokyo talks on the sex slavery could produce progress so that it could set the stage for improvement in bilateral ties.

The Seoul-Tokyo ties have plunged to the lowest levels in recent years mainly due to the sex slavery issue. Historians estimate the number of such sex slaves at about 200,000 with only 55 South Korean victims alive today.

In June, Japan angered Seoul and Beijing, both victims of Tokyo's wartime aggression, by saying that its 1993 apology over the sex slavery issue, named the Kono Statement, was the outcome of a political compromise between Seoul and Tokyo.

Abe said he will express remorse over Japan's role in the war in his fresh statement that will come around Aug. 15 to mark the 70th anniversary of Japan's defeat in World War II.

But analysts predict that the premier is not likely to apologize for the sex slavery issue and may water down the spirit of Japan's 1995 apology for Japan's colonial rule, named the Murayama Statement. (Yonhap)