U.S. National Security Adviser John Bolton will reportedly travel to South Korea later this week for a round of consultations ahead of U.S. President Donald Trump’s second summit with North Korean leader Kim Jong-un.

Quoting two administration officials, CNN reported on Wednesday that Bolton’s trip comes as top U.S. officials continue to hammer out the details of Trump’s summit with Kim. 

The report said South Korea is a critical partner in U.S. diplomacy with North Korea and that South Korean President Moon Jae-in has been the biggest proponent of Trump’s continued engagement with Kim.

CNN reported that Bolton has remained closely involved in policy discussions on North Korea, even as Secretary of State Mike Pompeo has been the diplomatic lead on the North Korea negotiations for the Trump administration. Bolton attended the first Trump-Kim summit in Singapore and was present for Trump’s discussions with Kim and other North Korean officials.