The U.S. State Department has reaffirmed that inter-Korean relations should progress in line with the denuclearization process.

An official at the department's Office of the Spokesperson made the remark on Wednesday when asked to comment about President Moon Jae-in's special envoys' latest trip to Pyongyang.

The official said that during the U.S.-North Korea summit in Singapore, Washington reaffirmed the Panmunjeom Declaration because improvement in cross-border relations must happen in lockstep with progress on denuclearization. 

The leaders of the two Koreas adopted the Panmunjom Declaration after their first summit in April, pledging to improve cross-border ties and pursue "complete denuclearization" of the Korean Peninsula. 

The state department official added that as President Moon Jae-in stated, the improvement of relations between North and South Korea cannot advance separately from resolving North Korea's nuclear program.