The United States has stressed that Seoul's voluntary declaration of its uranium enrichment experiment is not a cause for concern.

U.S. State Department spokesman Richard Boucher said Friday that Seoul is "cooperating fully and proactively in order to demonstrate that the activity has been eliminated and is no longer cause for concern."

Boucher added that Washington is "glad that South Korea's working in a transparent manner to do so."

He was quick to add, however, that although the scale of the enrichment is "much, much smaller" than in similar cases in North Korea and Iran, the experiment "should not have occurred and must be eliminated."

Boucher also said he does not think the revelation will have any impact on six-party talks over the North's nuclear program.