International Atomic Energy Agency (IAEA) staff arrived in North Korea on July 14 to monitor the Yongbyon nuclear complex, which the North closed as part of a disarmament pact reached in six-country talks in February.
"In doing our actions we had complete cooperation from the DPRK authorities," the head of the IAEA group, Adel Tolba, told reporters at Beijing airport after arriving from Pyongyang, capital of North Korea, or the Democratic People's Republic of Korea.
Tolba would not comment on the state of the North's nuclear facilities; such weighty issues are left to agency chief Mohamed ElBaradei, who is likely to issue a report on the shutdown in September.
But Tolba gave no sign of any problems.
"We think that what we need to perform was performed," he said. "We did perform all the mandated activities."
He said the team was heading back to its Vienna headquarters where an assessment would take place.
The 10 returning nuclear monitors are part of a "tag-team" who will watch over Yongbyon while six-party talks seek agreement on advancing the initial disarmament steps. A replacement team of six IAEA personnel arrived in North Korea earlier.
A reactor and uranium fuel processing plant at Yongbyon can produce the plutonium that North Korea used in its first nuclear test-blast in October last year.
North Korea halted the antiquated complex earlier this month after it began receiving heavy fuel shipments it was offered in return in the February deal.
The North also invited back IAEA personnel. They were thrown out of the country in late 2002 after a 1994 disarmament deal collapsed.
The next step of the disarmament deal, hammered out between North and South Korea, China, Japan, Russia and the United States, calls on Pyongyang to "disable" its nuclear facilities and provide a full accounting of its nuclear weapons programs.
Talks between the countries this month failed to produce a deadline for those steps.
They are to hold several sets of working-level talks in August and more senior meetings in September that could clear the way for implementation.