"We are prepared, along with the other four members of the six-party talks, to fulfill our obligations as North Korea fulfills its obligation, which includes disabling of the Yongbyon facility, as well as a declaration" of all its nuclear programs, State Department spokesman Sean McCormack said.

On the latest talks between US Assistant Secretary of State Christopher Hill and the DPRK's Vice Foreign Minister Kim Kye-Gwan in Singapore and Beijing, McCormack said "There's work that remains to be done."

The spokesman also noted that Hill's meeting with Kim "is not between the US and North Korea." "We are engaging them in the context of the six-party talks."

Under an agreement reached in October 2007 at the six party talks, the DPRK agreed to disable its key nuclear facilities at the Yongbyon complex, and to declare all other nuclear programs by the end of the year.

The six parties refers to the United States, the DPRK, China, South Korea, Japan and Russia.

The DPRK has denied that it had missed the deadline to submit that declaration, saying "other participating nations delay the fulfillment of their commitments, the DPRK is compelled to adjust the tempo of the disablement of some nuclear facilities on the principle of 'action for action'."