A senior U.S. diplomat says Washington is committed to strong ties with Seoul as the allies face a leadership transition in North Korea after Kim Jong Il's death. Assistant Secretary of State Kurt Campbell made the comments Thursday after meetings with South Korean officials in Seoul. Campbell says Washington is determined to be tightly aligned with Seoul as Kim Jong Il's son Kim Jong Un takes power in North Korea. Campbell is the highest-level U.S. official to visit the region since Kim's death. Also on Thursday, North Korea criticized South Korean President Lee Myung-bak for recently urging it to avoid provocation and stop nuclear activities.