Constructive relations between South Korea and Japan are a strategic priority for the United States, the State Department said Wednesday after the two American allies agreed to hold the first summit of their leaders in more than three years.

The planned summit between South Korean President Park Geun-hye and Japanese Prime Minister Shinzo Abe would mark the first bilateral summit between the two countries in about three and a half years and could serve as a turning point in their long-frayed relations.

The rare meeting is set for Monday in Seoul on the sidelines of a trilateral summit that also involves China.

"Constructive relations between Japan and the Republic of Korea, our most important allies in East Asia, are a strategic priority for the United States and help to advance peace and prosperity in the region," Katina Adams, a State Department spokesperson, said in response to a Yonhap News Agency request for comment on the summit agreement.

Relations between Seoul and Tokyo have been badly strained for years, due mainly to Tokyo's attempts to whitewash its wartime atrocities and colonial occupation, especially its sexual enslavement of women for its troops during World War II.

The two countries held their last summit, between then-President Lee Myung-bak and Japanese Prime Minister Yoshihiko Noda, in May 2012. Park and Abe have never held such a meeting as Tokyo has refused to accept Seoul's demand that it formally apologize to and compensate victims of its wartime sexual slavery.

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, seen as a key pillar for President Barack Obama's "pivot to Asia" initiative, aimed in part at keeping a rising China in check. (Yonhap)