The Republic of Korea's foreign minister, Yun Byung-se, will visit Tokyo on Sunday, the first such trip in four years, as the US allies prepare to mark the 50th anniversary of the normalization of ties amid a chill because of feuds over the wartime past.

Yun will meet Japanese Foreign Minister Fumio Kishida on Sunday and attend a ceremony at the ROK embassy the next day, the anniversary of a 1965 treaty normalizing diplomatic ties, the ROK Foreign Ministry said on Wednesday. The visit was simultaneously announced in Tokyo.

Relations between Japan and the ROK have been cool mainly because of disputes over the legacy of World War II and Japan's 1910-45 annexation of the Korean Peninsula.

The issue of "comfort women" - a euphemism for women in Japanese-occupied territory who were forced to work in wartime military brothels - has been especially thorny. The neighbors are also locked in a dispute over tiny islands that lie between them.

In an interview with The Washington Post last week, ROK President Park Geun-hye said there had been "considerable progress" on the issue of the women forced to work as prostitutes, and the two sides were "in the final stage of our negotiations". She did not elaborate. ROK officials have said there had been "meaningful progress" in high-level discussions between the two countries over the women.

However, a Japanese government source with knowledge of the matter said there had been little progress, and a breakthrough appears unlikely when Yun comes to Tokyo.

"We will of course welcome the Korean foreign minister cordially and warmly ... but I don't know how much progress we will be able to make because we don't see any sign of flexibility on the Korean side," the official told Reuters.

The "comfort women" issue has long been a thorn in ties.