Kim Yong Chul, the vice-chairman of the Party Central Committee, has represented Kim Jong Un at key events this year, and is the young leader's top official in charge of relations between North and South Korea. His trip to the US was confirmed by Trump, who wrote in a tweet on Tuesday morning that Kim was traveling to New York. He called the North Korean leader's decision to send one of his top lieutenants a "solid response to my letter, thank you!"On his arrival in the US, Kim would be the most senior official to visit the United States since 2000, when Vice Marshal Jo Myong Rok traveled to Washington to meet with then-President Bill Clinton in the Oval Office. Madeleine Albright, who was Secretary of State at the time, traveled to North Korea later that month.Kim Yong Chul is a former head of North Korea's Reconnaissance Bureau, an espionage and special operations organization. He is believed to have been involved in a torpedo attack that sank the South Korean warship Cheonan in 2010, killing 46 South Korean sailors.His inclusion as part of the delegation from the North that attended the Pyeongchang Olympics in February raised eyebrows given his suspected role in the Cheonan's sinking. Kim's latest trip comes as the United States and North Korea attempt to revive the summit between the countries' two leader, a potential diplomatic triumph for nations technically still at war."He is probably one of the most up-to-date North Korean officials about what North Korea's requirements are for the summit," said Catherine Dill, a senior research associate at the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies at Monterey in Calilfornia."I think it's a pretty big deal and to me this raises whatever the estimates were of the summit actually occurring," she told CNN.Trump indicated in his tweet that meetings were currently taking place "concerning the summit and more." North Korean and US officials have been spotted at hotels in Singapore, where the two leaders had been planning to meet.Kim Yong Chol's trip to the US indicates that Washington and Pyongyang have direct lines of communication open and are working closely together to work though issues ahead of the summit.Together with Kim Jong Un's sister Kim Yo Jong, Kim Yong Chol has been regularly photographed by the North Korean leader's side. He attended both recent meetings with South Korean President Moon Jae-in at the demilitarized zone.Kim Yong Chol has also already met at least one senior US official — he was pictured greeting US Secretary of State Mike Pompeo when the former CIA director visited Pyongyang earlier this month.