Uranium traces reportedly found on papers from North Korea

The United States in recent weeks has obtained new intelligence -- fresh traces of highly enriched uranium discovered among 18,000 pages of North Korean documents -- that is raising questions about whether Pyongyang pursued an alternative route to producing a nuclear weapon, according to sources familiar with the findings.

Officials at the State Department and with the director of national intelligence declined to comment.

North Korea is known to have used plutonium in its nuclear weapons program, a different route from using uranium enrichment.

Pyongyang has insisted that it had no uranium-enrichment program.

Late last year, U.S. analysts unexpectedly found traces of enriched uranium on smelted aluminum tubing they said could be used as the outer casing for centrifuges needed to spin hot uranium gas into the fuel for nuclear weapons.

Now, the fresh samples of enriched uranium complicate the issue. Sources said that traces of highly enriched uranium were found on the 18,000 pages of records from the Yongbyon reactor provided by North Korea to the United States last month.

North Korea handed over the documents, which date to 1987, to help the United States verify the amount of plutonium produced in the reactor. But the documents have become central to the debate over Pyongyang’s possible enrichment activities.