North Korea's efforts to disable its plutonium-producing reactor by year's end are going as scheduled, the top US nuclear envoy said Wednesday, but work needs to continue if deadlines are to be met. US Assistant Secretary of State Christopher Hill spent two days in Pyongyang and visited the Yongbyon nuclear complex, becoming the highest-level American official to go there. "The disablement activities are going well and on schedule," Hill told reporters before leaving Pyongyang and heading to Beijing. "I'm satisfied with the results." "But," he said, "we have to keep working because we have more to do to meet our deadlines."