The UN nuclear watchdog head has arrived in North Korea and said he is hopeful progress can be made on closing its atomic facilities.
Inspectors from the International Atomic Energy Agency have not visited North Korea since the hermit state expelled them in late 2002 as a disarmament deal fell apart.
The impoverished nation agreed to admit the watchdog as part of a new accord reached in February this year.
The IAEA will play a key role in verifying whether it meets a commitment to shut down the Yongbyon reactor at the heart of its nuclear programme.
"I hope we should be able to make some progress," IAEA head Mohamed ElBaradei told reporters before leaving Beijing.
He hoped his agency could "work closer with the DPRK after many years of estrangement", referring to the North by its official name, the Democratic People's Republic of Korea.
Under the February deal, cut at six-party talks in Beijing that group the two Koreas, the US, China, Japan and Russia, North Korea agreed to shut Yongbyon by mid-April in return for an infusion of energy aid and security assurances.
"This is an important part of the six-party talks' implementing of the initial steps," Mr ElBaradei said of his trip.
"I think obviously these initial steps will be important, significant in fact, in moving the six-party talks forward."
One US official expressed confidence that North Korea would make good on its pledge to shut down Yongbyon.
"It can be done in a short period of time (and) we're reasonably confident they will take that step," the official said.
But others said it was still too soon to make predictions.
"My understanding is that some of what we have seen in recent weeks is maintenance and the like, but we'll have a better idea after ElBaradei visits this week," a second US official said.