South Korean President Park Geun-hye said Prime Minister Shinzo Abe missed an opportunity to improve ties between their countries by not apologizing for Japan's wartime use of sex slaves during his U.S. trip.

"There is much criticism, even in the U.S., about the Abe government not taking advantage of the chance to strengthen trust with neighboring nations with a sincere apology over historical issues, including the (wartime) 'comfort women' victims," Park said Monday at a meeting with secretaries, according to her office's website.

Park's demands that Abe do more to atone for Japan's wartime aggression have added to tensions over the Takeshima-Dokdo territorial dispute and soured South Korea-Japan relations. The rift between the two biggest U.S. allies in North Asia is complicating President Barack Obama's shift to Asia and his effort to maintain a united front to contend with a nuclear North Korea and a more assertive China.