The U.S. is urging Japan and South Korea to improve strained relations, which Washington fears may threaten an important Asian security alliance.
Danny Russel, the top U.S. diplomat on East Asia, called on both countries to "show prudence and restraint in dealing with difficult historical issues."
"It is very much in the interest of the United States and therefore it is very much a diplomatic priority for the United States that the friction and the tension between these two extraordinarily close friends and allies of the United States be reduced - and be reduced quickly. Both Japan and the Republic of Korea need to make respective efforts to help create a more conducive and positive climate."
Relations between the two U.S. allies have plummeted over what Seoul considers Tokyo's unapologetic stance toward Japan's imperialist past.
Russel said both countries share many of the same challenges, including North Korea and its nuclear weapons program and other "regional uncertainties."
This week, Japan announced it will review evidence that led to a 1993 apology over forced prostitution of Asian women in Japanese wartime brothels.
South Korean President Park Geun-hye has said that Tokyo will only experience isolation if it revises the apology for the so-called comfort women.
As many as 200,000 Asian women, mainly South Koreans, were forced to serve as sex slaves for Japanese soldiers during World War 2.
Seoul also responded angrily to a visit last year by Japanese Prime Minister Shinzo Abe to a Tokyo shrine that honors several war criminals among other war dead.
Senator Ben Cardin, who chairs the Senate Foreign Relations Committee's East Asia subcommittee, said Mr. Abe's "rhetoric on these issues is increasingly concerning to many."
He also said Beijing, which has its own historic disputes with Tokyo, may be trying to take advantage of the situation.
"One of my concerns is that it looks like China is trying to increase the wedge between Japan and the Republic of Korea to establish a closer relationship with the Republic of Korea to the detriment of Japan."
China has complained fiercely over Mr. Abe's visit to the Yasukuni Shrine, as well as his stated intention to change or reinterpret Japan's pacifist construction.
South Korea and China were among the primary victims of Japan's pre-war imperialism. Both are also engaged in tense territorial disputes with Japan.