In June, a planned intelligence-sharing pact between Japan and South Korea was derailed. Then in August, a visit by South Korea's outgoing President Lee Myung-bak to small islands claimed by both nations led to angry exchanges between Tokyo and Seoul.
Perceptions in Seoul that Abe wants to minimize or whitewash Japan's wartime past also threaten to undermine the relationship. Abe has suggested that Japan's landmark 1993 apology for the suffering of World War II sex slaves, many of them Korean women, needs revising.
Campbell said the visit by U.S. officials was to ensure both governments are committed to "rebuilding" their ties.
Signaling Tokyo's determination to expand its trade and investment with other Asia-Pacific nations, Abe dispatched his foreign minister, Fumio Kishida, on visits to the Philippines, Singapore, Brunei and Australia this week.
Abe himself will be making his first trip abroad next week to Southeast Asia, with plans to visit Indonesia, Vietnam and Thailand to strengthen ties already growing as Japanese manufacturers boost investments and marketing in the region.
"These three countries are engines for growth of the world economy," chief government spokesman Yoshihide Suga told reporters Thursday. He deflected suggestions that Tokyo was seeking to counterbalance China.
"I don't view respecting relations with the rest of Asia as a countermeasure against China," he said.
Associated Press writers Christopher Bodeen in Beijing and Mari Yamaguchi in Tokyo contributed to this report.
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