North Korea's claim of a new, highly sophisticated uranium enrichment facility could be a ploy to win concessions in nuclear talks or an attempt to bolster leader Kim Jong Il's apparent heir.

But whatever the reason for the revelation, which a seasoned American nuclear scientist called "stunning," it provides a new set of worries for the Obama administration, which is sending its special envoy on North Korea for talks with officials in South Korea, Japan and China this week.

The scientist, Siegfried Hecker, said in a report posted Saturday that he was taken during a recent trip to the North's main Yongbyon atomic complex to a small industrial-scale uranium enrichment facility. It had 2,000 recently completed centrifuges, he said, and the North told him it was producing low-enriched uranium meant for a new reactor.

Hecker, a former director of the U.S. Los Alamos Nuclear Laboratory who is regularly given rare glimpses of the North's secretive nuclear program, said the program had been built in secret and with remarkable speed.

Adm. Mike Mullen, chairman of the U.S. Joint Chiefs of Staff, said uranium enrichment activities would violate U.N. resolutions and agreements by North Korea over its nuclear program.