The United States confirmed Monday that North Korea missed a year-end deadline for declaring all its nuclear programs and assets under last year's aid-for-disarmament deal. But the State Department is not expressing alarm over the development and says efforts to implement the accord will continue. VOA's David Gollust reports from the State Department.

Spent nuclear fuel rods at a nuclear facility in Yongbyon, North Korea (File)

Pyongyang's failure to meet the deadline for full nuclear disclosure is not the first snag in the complex disarmament deal, and officials here say other elements of the process will proceed as the parties prod North Korea to fully account for its nuclear activities.

North Korea was obligated to declare, among other things, how many nuclear weapons it produced and what nuclear assistance it may have obtained from or given to other countries. The United States has also pressed for an accounting of the secret uranium enrichment project it believes North Korea was conducting in the 1990s in addition to its acknowledged plutonium-based weapons program.

State Department Deputy Spokesman Tom Casey said the midnight, North Korea time, deadline for the declaration had passed without any last minute submission from the Pyongyang government.

The development had been anticipated, with the United States, Japan and South Korea having made a coordinated expression of disappointment several hours before.

Spokesman Casey said the lack of a timely declaration is "unfortunate" but that diplomacy aimed at fulfilling that and other elements of the agreement will move forward.

"The important thing is not whether we had the declaration by today or not," he said. "The important thing is that we get a declaration that meets the requirements of the agreement, which means it needs to be full and complete. Again, we've had ample discussions with the North Koreans about what that is. Certainly we're going to continue to talk with other parties including the North Koreans about this, and we do expect that they will in fact meet this obligation and provide us with a declaration."

North Korea agreed in principle in 2005 to give up its nuclear program in return for aid and diplomatic benefits.

Under the detailed accord reached last February at the Chinese-sponsored six-party talks, Pyongyang is getting one million tons of heavy fuel oil and equivalent aid in exchange for shutting down and permanently disabling its Yongbyon nuclear reactor complex.

Casey said there has been good progress in fulfilling some elements of the agreement, though he said the process of disabling the Yongbyon reactor is behind schedule, because of safety issues in removing radioactive fuel rods from the facility.

He said having a full and complete accounting of North Korean nuclear activities is essential for the final phase of the agreement, which includes dismantling the program and creating new regional security arrangements.

"This can't be a situation where they pretend to give us a full declaration and we pretend to believe them," he said. "This has to be full and complete. That's why, I think, this is taking extra time, and it's important that what we get in the end from the North Koreans is something everyone can feel comfortable is really a full and complete declaration and contains all the elements of their nuclear programs."

Casey said he expects Assistant Secretary of State for East Asian Affairs Christopher Hill, the chief U.S. delegate to the nuclear talks, to consult separately with other envoys later this week on the declaration issue.

He said there are no immediate plans for a joint meeting of all six parties, which include Russia, Japan, South Korea and the United States in addition to North Korea and host China.