Russia thanked for role in N Korean talks
Pyongyang has already shut its main nuclear reactor at Yongbyon.
The latest discussions are focused on firming up North Korea's commitment to fully disarm.
In return for fuel aid the communist country is expected to disable all atomic activities.
It must also account for shipments, which Washington claims, prove they were trying to build nuclear weapons.
Despite several positive steps, negotiators have warned many possible pitfalls remain.