Andrew Kim, head of the CIA's Korea Mission Center, was in Seoul for a four-day visit that started Wednesday and has returned to the US after holding talks with officials from both sides, according to the sources.
Kim's secret visit is presumed to have been aimed at narrowing the differences between Washington and Pyongyang over the process for the North's denuclearization ahead of planned talks with US Secretary of State Mike Pompeo and Kim Yong-chol, vice chairman of the North's ruling Workers' Party of Korea later this month.
The North has sought US concessions vis a vis its demands for a declaration of a formal end to the Korean War -- apparently as a way to guarantee its regime security -- and sanctions relief.
But the US has insisted that Pyongyang should first take concrete measures, such as a full declaration of its nuclear and missile programs, before any rewards could be given.
Kim, a Korean-American, is known as a close aide of Pompeo with a deep knowledge of North Korea who played a key role in the June summit between US President Donald Trump and North Korean leader Kim Jong-un.
Washington and Pyongyang have been seeking to arrange a second summit between their leaders, amid a lack of progress in negotiations on Pyongyang's denuclearization. (Yonhap)