North Korea has failed to meet a deadline to disclose details of its nuclear programme by the end of 2007.
North Korea started disabling Yongbyon in October
Pyongyang had pledged to provide a detailed declaration of its nuclear activities by 31 December, but the US has confirmed it has not yet done so.
South Korea, Japan and the US have all expressed disappointment at the North's failure to meet the deadline.
The agreement was part of a disarmament deal under which Pyongyang is to receive large amounts of aid.
The North agreed to the deal during six-party talks in February. The nations involved in the process are China, the US, Japan, Russia and the two Koreas.
The North began disabling Yongbyon in October, in a process overseen by US experts.
While the disablement has not been completed in time for the end-of-year deadline, analysts say the delay is mainly due to technical problems.
Of more concern is the delay in producing a written declaration of the North's nuclear activities - which analysts say is a key indicator of whether the North intends to stick to its promise to become nuclear-free.
As the deadline loomed, various nations expressed their disappointment at the lack of progress in this area.
Japan's foreign ministry described the lack of a declaration as "unfortunate", and said the North Koreans should provide one "at the earliest possible date".
South Korea's foreign ministry had a similar message for its Northern counterparts, urging them to "faithfully declare all nuclear programmes at an early date, and complete disablement steps without delay".
As the deadline passed, US State Department spokesman Tom Casey said: "There has been no last-minute change... It's unfortunate but we are going to keep on working on this.
"I expect there will be some consultations on this over the next few days, among the parties, to see how we want to proceed from here."
The US particularly wants to know how much plutonium has been produced by North Korea, and also to see evidence that there is no secret programme for uranium enrichment for weapons purposes.
Earlier this month, US President George W Bush sent a personal letter to the North Korean leader, Kim Jong-il, urging him to honour its pledge at the six-party talks.
The letter was delivered by US chief envoy Christopher Hill, who visited North Korea earlier this month to assess progress.
After visiting the facility, Mr Hill said the disablement activities were "going well and on schedule".