Kim Yong Chol was once blacklisted by the United States for his role in his country's military establishment.
The senior Korean official had been in New York City for meetings with US Secretary of State Mike Pompeo about preparations for a summit between Trump and Kim.
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Earlier in the day, the head of the US delegation for summit preparations and US ambassador to the Philippines said that the talks on preparations for the summit between US President Donald Trump and North Korean leader Kim Jong-un were showing progress.
Nevertheless, Washington and Pyongyang have continued making preparations for the historic summit, which might be focused on denuclearization as well as bringing peace to the Korean Peninsula.