US Under Secretary of State Wendy Sherman called in both the South Korean and the Japanese ambassadors to Washington for separate meetings in a possible sign that the US is stepping up efforts to help improve relations between the two key Asian allies, Yonhap news agency reported.

Sherman met with South Korean Ambassador Ahn Ho-young on Friday morning and discussed various issues, including historical tensions and the North Korean nuclear standoff, for about an hour, a diplomatic source said. She held a similar meeting with Japanese Ambassador Kenichiro Sasae later in the day.