A diplomatic source says that North Korea has admitted to importing 150 tons of high-strength aluminum tubes from Russia in connection with its suspected uranium enrichment activities that triggered the second nuclear standoff in 2002.

The source said the North didn't say, however, where the tubes were used or where they are now. But the source quoted the North as saying that it will address the matter when it reports all of its nuclear programs in the second stage of denuclearization.

The North's confession came during working group talks with the U.S. in Geneva early this month while discussing highly enriched uranium, a key concern in the North's report of its nuke programs.

High-strength aluminum tubes are used in making cases for centrifuges, which can be used in uranium enrichment.

It's the first time that Pyongyang has admitted to the import of such materials. Its willingness to specify the amount is seen as a show of its sincere will to carry out the reporting process.