The United States is speculating that North Korea has "at least one other" uranium enrichment facility in addition to the one it showed to American experts last month.

State Department spokesman Philip Crowley told reporters Tuesday that Washington "is very conscious of the fact that, in the recent revelations to American delegations, what they saw did not come out of thin air." He then said that the North’s revelation suggests that work is being done in at least one other site.

Following a trip to the North by former director of the Los Alamos National Laboratory Siegfried Hecker last month, Washington has raised suspicions that the North has another uranium enrichment site other than the one it disclosed to Hecker. Hecker said that during his trip, North Korean officials showed him a uranium enrichment facility at the Yongbyon nuclear site with two-thousand centrifuges.