U.S. Assistant Secretary of State Kurt Campbell said North Korea’s return to the six-party talks is a priority and an essential step.

Campbell said at a news conference following his meeting with Deputy Foreign Minister Lee Yong-joon on Wednesday that positive developments in inter-Korean relations are important and the U.S. welcomes Seoul’s efforts for a summit with the North. However, he said that what is essential is Pyeongyang’s return to the six-party talks for the disarmament of North Korea.

He added that although it is possible to discuss other issues, including a peace treaty, within the six-way talks framework, there must also be progress with the denuclearization.

On the Korean American missionary Robert Park, who is being detained by North Korea after voluntarily entering the Stalinist state late last year, Campbell said Park appeared to have been moved to Pyeongyang and the U.S. is seeking an approach through diplomatic means.

At a separate news conference on Wednesday morning, the Assistant Secretary of State said that due to the strong alliance between the U.S. and South Korea, the U.S. is taking into serious consideration the South’s concerns regarding the transfer of wartime operational command.