A senior U.S. official said Tuesday that the United States has been "very flexible" in its defense cost-sharing negotiations with South Korea, and it is looking for some flexibility from the Korean side as well. 

Deputy Assistant Secretary of State for Korea and Japan Marc Knapper made the remarks during an online forum hosted by the Center for Strategic and International Studies. 

Knapper said the leaders of the two nations have spoken recently, and the two sides will continue to look for ways to sit down and talk, noting the COVID-19 pandemic has made it difficult for face-to-face negotiations. However, he refused to elaborate on details, citing policy not to discuss them in public. 

Meanwhile, Knapper said that the U.S. closely cooperated and shared information with its allies South Korea and Japan on North Korean leader Kim Jong-un's recent disappearance from public view. 

He said that the most recent curiosity involving Kim's disappearance definitely invited a lot of good, close info-sharing and coordination between the U.S. and its colleagues in both Seoul and Tokyo.