South Korea's national security advisor said on Thursday that the declaration of a formal end to the Korean War cannot be separated from the denuclearization process of the Korean Peninsula, adding it is "common sense" that the two issues go together.

Suh Hoon, director of South Korea's National Security Office, made the remarks to reporters after his meeting with U.S. Secretary of State Mike Pompeo at the State Department in Washington.

The security adviser said declaring the war's end is not a new issue, adding it has always been on the negotiating table and there can be no different views regarding the issue between South Korea and the U.S.

Suh said the only issue is when the declaration should be made in the process to denuclearize North Korea and how closely it should be tied to the process. 

He said, however, that there were no in-depth talks on the matter during his trip. 

The national security adviser said he did not have any serious discussions on the issue of defense cost-sharing with his U.S. counterparts during the trip, but that the government will continue to discuss the issue. 

He added that it's desirable for the two sides to reach an agreement at a reasonable and mutually acceptable level as soon as possible.