U.S., South Korea pledge unity on sanctions against North Korea SEOUL, March 16 (UPI) -- U.S. Secretary of State John Kerry and South Korean Foreign Minister Yun Byung-se agreed Saturday to cooperate on implementing sanctions against North Korea. Kerry and his South Korean counterpart spoke by telephone in advance of Kerry's planned visit to the nation next month, Yonhap News Agency said. The leaders pledged to move forward with implementation of a tough new round of sanctions against North Korea ordered by the United Nations Security Council following the North's most recent nuclear test explosion. Kerry will visit the Korean peninsula, China and Japan in April. His visit to Seoul paves the way for a planned summit in May between U.S. President Barack Obama and newly elected South Korean President Park Geun-hye.