The U.S. has reaffirmed its position that developments in inter-Korean relations should be in parallel with North Korea's denuclearization process.

The remarks by a State Department official Thursday were made in regards to the opening of the two Koreas' liaison office in the North's Gaeseong Industrial Complex on Friday.

The official said the leaders of the U.S. and North Korea reconfirmed April's inter-Korean summit declaration in Singapore, which includes the launch of the liaison office, since improved inter-Korean ties should work in concert with denuclearization.

Citing South Korean President Moon Jae-in, the official also said that advancement in inter-Korean ties cannot proceed separately from Pyongyang's denuclearization.