The chief of a U.S.-led nuclear expert team says the disablement of three key nuclear facilities in Yongbyon has begun, adding that this week will see the completion of at least one of eleven disablement steps.

Arriving at Incheon International Airport Tuesday after witnessing the start of North Korea's nuclear disablement, State Department official Sung Kim told reporters that the process is off to a very good start.

Kim also said that he urged Pyongyang to maintain the pace and to complete disablement by year’s end.

The State Department’s Korea Desk director will brief Seoul officials on the latest in the disablement process and attend the annual Security Consultative Meeting of U.S. and South Korean defense chiefs on Wednesday.