The United States reacted cautiously Sunday to signs of a thaw emerging in the long-chilled relations between South Korea and Japan as their leaders agreed to visit each other's embassy to celebrate the 50th anniversary of the normalization of diplomatic relations.

South Korean President Park Geun-hye plans to attend an anniversary ceremony to be held at the Japanese Embassy in Seoul on Monday while Japanese Prime Minister Shinzo Abe also plans to visit the Korean Embassy in Tokyo for a similar ceremony, both sides announced.

In addition, South Korean Foreign Minister Yun Byung-se made his first-ever visit to Tokyo since taking office and agreed with his Japanese counterpart, Fumio Kishida, to smoothly resolve the dispute surrounding Japan's bid to list some of its wartime industrial complexes as UNESCO World Heritage sites.

The bid was the latest source of historical tension between the two countries because some of the facilities are where a number of Korean slave laborers toiled during Japan's 1910-45 colonial rule.

Sunday's agreement was seen as a sign that Japan will accept South Korea's demand and reveal the slave labor history in UNESCO records.

Despite these positive moves, reaction from the U.S. was lukewarm.

"We believe that good relations among countries in the region promote peace and stability and are in their interests and in the interests of the United States," a State Department representative said on background in response to a Yonhap News Agency request for comment.

Though the comment is in line with the long-standing U.S. position on the issue, the official stopped well short of welcoming the latest agreements between Seoul and Tokyo. The official did not even mention Korea or Japan by name, and referred further queries to the governments of South Korea and Japan.

It is unclear why the U.S. is taking such a cautious stance on the issue.

Washington has put in a lot of effort to have the two key Asian allies to come to terms with each other, with U.S. President Barack Obama even hosting a three-way summit with Park and Abe in an attempt to get the leaders to hold a face-to-face meeting.

Frayed relations between the two allies have been a key cause for concern for the U.S. as it seeks to bolster three-way security cooperation as a key pillar for Obama's "pivot to Asia," aimed in part at keeping a rising China in check. (Yonhap)