Published: Nov 21, 2010 9:20 PM EST
Updated: Nov 21, 2010 6:20 PM EST

SEOUL, South Korea (AP) - The Obama administration is facing a new set of worries about North Korea.
      
A scientist who recently visited the north says a new, highly sophisticated uranium enrichment facility has been built there -- secretly, and with remarkable speed.
      
The development comes as the White House sends its special envoy on North Korea for talks with officials in South Korea, Japan and China this week.
      
The chairman of the Joint Chief of Staff, Adm. Mike Mullen, tells CNN that it's just another step by North Korea toward "destabilizing the region." He says it confirms the fears the U.S. has had for years about North Korea's nuclear activities.
      
As for why North Korea is letting the world know about this facility now, a South Korean professor says it seems to be an effort to force the United States back into nuclear negotiations.  He says it's also an attempt by the North to build loyalty in its military brass during a change of leadership.
      
The Obama administration has rejected direct talks with North Korea following its nuclear and missile tests last year, and after an international finding that a North Korean torpedo sank a South Korean warship in March, killing 46 sailors.

(Copyright 2010 by The Associated Press.  All Rights Reserved.)