A US-led team of experts has arrived in North Korea to oversee the dismantling of the country's nuclear programme.
Sung Kim is leading the team of experts in Pyongyang
They are due to map out a plan for disabling the reactor at Yongbyon, which US officials believed capable of producing weapons-grade plutonium.
Pyongyang has agreed to shut its main facilities and give complete details of its nuclear programme by 31 December.
The agreement came after negotiations last month in Beijing involving China, the US, Japan, Russia and the Koreas.
The experts, led by Sung Kim of the US state department, landed in Pyongyang on a flight from Beijing on Thursday.
Before boarding the flight, Mr Kim told the Associated Press he was "looking forward to a very productive visit".
"We expect to be there for a week or so to finalise discussions on disablement, the scope of disablement and also to discuss a wide range of administrative issues," he said.
Pyongyang, which tested a nuclear device last year, has already shut down several facilities in return for aid.
The North's rulers also hope their co-operation on the nuclear issue will lead to the country's removal from the US list of state sponsors of terrorism.