SEOUL, South Korea — The leaders of South Korea and Japan attended separate ceremonies Monday in their respective capitals marking the 50th anniversary of the resumption of normal ties — small, mostly symbolic moves that could signal an easing of abysmal relations between the key U.S. allies.

The United States, which sees the neighbors as important military and diplomatic bulwarks in its regional strategy, will welcome the visits by South Korean President Park Geun-hye to a Japan-organized event in Seoul and Japanese Prime Minister Shinzo Abe to a South Korea-organized event in Tokyo.

It is unclear, however, how much will actually change between the neighbors amid lingering bad feelings seven decades after Japan's World War II surrender.

Many in Seoul are uncomfortable with what's seen as Abe's right-wing tilt and Tokyo's push to whitewash its brutal colonization of the Korean Peninsula from 1910 to 1945. Some in Japan have expressed fatigue and frustration with South Korea's perceived refusal to recognize Japan's previous efforts at reconciliation.

South Koreans complain about Japan's perceived refusal to deal fairly with the issue of women forced by the Japanese military into sexual slavery during Tokyo's colonization and World War II, and over disputed islets occupied by South Korea but claimed by Japan.

Since taking office in early 2013, Park has not held official one-on-one talks with Abe, although President Barack Obama brought them together for a three-way meeting last year.

Park, in a message read by her foreign minister during the Tokyo event, said the two countries must work together this year to open a new era of cooperation by resolving historical issues that she described as "the biggest obstacle" to better ties, according to her office.

The two leaders have faced calls at home and abroad to improve ties. Their countries are closely linked economically and are crucial to U.S. military and diplomatic interests in the region. Washington wants Seoul and Tokyo to help the U.S. deal with a rising China and with nuclear threats from North Korea.

Between them, Japan and South Korea host about 80,000 U.S. troops, the core of America's military presence in the Asia-Pacific.

Abe, in his speech in Tokyo, vowed to cooperate with Park and said economic, cultural and people exchanges between the two countries over the past 50 years have become "invaluable assets."

Associated Press writer Mari Yamaguchi in Tokyo contributed to this report.