"We don't have any indication that they will not provide" a declaration, she added. "But they missed the deadline and we are waiting to hear from them."
Sean McCormack, a state department spokesman, said the US would continue to press North Korea to deliver on its commitments.
"We're going to keep hammering away at it. We're not lowering the bar"
Sean McCormack, US state dept
"We're going to keep hammering away at it. We're not lowering the bar," he said.
"North Korea has to come out with a full and complete declaration.
"We are still committed to fulfilling our obligations under the agreement, under the idea of action for action," McCormack said, adding that the dismantling of the North's main plutonium-producing reactor was still proceeding despite a delay for technical reasons.
North Korea promised in February that it would abandon its nuclear weapons programme in return for energy aid and political concessions.
In October, it pledged to disable its nuclear facilities and declare its programmes by the end of the year.
And under the watch of US experts in November, it began to disable its sole functioning atomic reactor in Yongbyon – which it shut down in July – along with other facilities.
North Korea did not mention the missed deadline on Tuesday when it issued a statement calling on the US to scrap its "hostile" policies towards the Asian nation.
The US wants the North Korean declaration to address a suspected secret uranium enrichment programme, a sticking point that sparked the latest nuclear standoff in late 2002.
In an apparent drive to keep the disarmament process on track, Christopher Hill, the chief US nuclear negotiator, will make a "Northeast Asia tour" beginning at the end of the week, McCormack said.
The itinerary for the visit has not yet been released.
At the same time US officials say John Negroponte, the deputy secretary of state, will take up the declaration issue in talks with Chinese leaders in Beijing at regularly scheduled talks in mid-January.
Diplomats had said for weeks that North Korea would probably miss the year-end deadline for disabling its nuclear facilities because a key technical step - removing fuel rods safely from the Yongbyon reactor - could take months.
But according to a report by Japan's Kyodo News, the North has also told the US it is reducing the shifts of workers carrying out the American-financed operation.
A Pyongyang official reportedly warned last week of a slowdown because of a delay in providing the promised energy aid.
The US, Japan and South Korea - members of the negotiations along with Russia, China and the North itself - expressed disappointment at the missed deadline but have been relatively muted in their reaction.