State Department spokesman Sean McCormack said in a statement that the DPRK must "realize fully its commitments ... by inviting back the IAEA immediately to begin shutting and sealing the Yongbyon nuclear facility."

The statement followed the visit of a U.S. delegation led by New Mexico Governor Bill Richardson and former veteran affairs secretary Anthony Principi, to Pyongyang earlier this week to ask the DPRK to fulfill its obligations under a February deal to shut down the unclear facility.

However, the statement did not mention the fact that Washington failed to resolve a dispute over DPRK funds frozen through U.S. sanctions as part of the deal.

The DPRK has made it clear that it will allow IAEA inspectors back and shut down the nuclear facility only after it confirms that the funds were released.

The DPRK funds were frozen after the United States blacklisted the Banco Delta Asia bank of Macao for allegedly helping Pyongyang launder money, an allegation the bank has denied.

The dispute over the frozen funds has put a gloomy prospect over the nuclear facility issue.