Special US envoy Stephen Bosworth visiting South Korea

The Obama administration's special envoy on North Korea plans to visit South Korea, Japan and China, officials said Sunday.

Stephen Bosworth's trip comes as new satellite images show construction under way at North Korea's main atomic complex. That, combined with reports from two American experts who recently travelled to the Yongbyon complex, appear to show that Pyongyang is making good on its pledge to build a nuclear power reactor.

Bosworth is to arrive in Seoul on Sunday for a two-day trip aimed at discussing the North's nuclear weapons program. The U.S. State Department said in a statement that Bosworth will then travel on to Tokyo and Beijing before flying back to Washington later this week.