General Kim Yong Chol, vice chairperson of the central committee of the Workers' Party and right-hand man to Kim, will meet US Secretary of State Mike Pompeo in New York on Wednesday or Thursday, officials said.
Trump confirmed the general was on his way in a tweet and boasted that Washington would have a "great team" for the talks on resolving the old foes' nuclear standoff. The president still hopes the meeting will take place on June 12 in Singapore.
Senior North Korea envoy to hold talks in US about summit
"Meetings are currently taking place concerning Summit, and more. Kim Young Chol, the Vice Chairperson of North Korea, heading now to New York. Solid response to my letter, thank you!" Trump wrote.
Trump will also meet Japan's Prime Minister Shinzo Abe in Washington on June 7, White House spokesperson Sarah Sanders said.
"Since the president's May 24 letter to North Korean leader Kim Jong Un, the North Koreans have been engaging," she said. "The United States continues to actively prepare for President Trump's expected summit with leader Kim in Singapore."
A spokesperson for the North Korean mission to the United Nations said he was unable to confirm that the general was on his way to New York but added that "preparation for the summit is proceeding at the highest level."
The North Korean envoy landed at Beijing airport on Tuesday and was to meet with Chinese officials before traveling on to the United States on Wednesday, according to South Korea's Yonhap news agency.
Pompeo's spokesperson said it would be the third meeting between Pompeo - who opened contacts with the isolated Pyongyang regime when he was still CIA director - and General Kim.
"The secretary will be heading up to New York tomorrow and I believe returning some time on Thursday," she said. "We're still finalising exactly what these meetings will look like."
The trip is part of a flurry of diplomacy before the on-again, off-again summit.
Trump briefly scrapped the talks last week, citing "open hostility" from the North, but since then both sides have dialed down the rhetoric and the process appears to be back on track.
On Sunday, US negotiators, headed by Washington's ambassador to the Philippines Sung Kim, began meeting North Korean counterparts in the truce village of Panmunjom that divides the two Koreas.
"They plan to have additional meetings this week," Sanders said.
She said White House Deputy Chief of Staff Joe Hagin and a US team are separately coordinating logistics in Singapore for the expected summit.
Chung Sung-yoon, an analyst at the Korea Institute for National Unification, said Kim Yong Chol would be the most senior North Korean on US soil since Vice Marshal Jo Myong Rok met then president Bill Clinton in 2000.
The general has played a front-seat role during recent rounds of diplomacy aimed at ending the nuclear stalemate on the Korean peninsula.
He sat next to Trump's daughter Ivanka, who is also a White House aide, during February's closing ceremony for the Winter Olympics in South Korea, an event that was seen as a turning point in the nuclear crisis.
He also accompanied Kim Jong Un on both of his recent trips to China to meet President Xi Jinping, and held talks with Pompeo when he traveled to Pyongyang.
General Kim is a notorious figure in South Korea, where he is blamed for masterminding the 2010 sinking of the Cheonan navy corvette that killed 46 sailors, an attack for which North Korea denies responsibility.
From 2009 to 2016, he also headed North Korea's General Reconnaissance Bureau, the unit tasked with cyber warfare and intelligence gathering.
During that period, North Korea ramped up its hacking programs, including a hugely costly penetration of Sony Pictures.
General Kim is one of several North Korean officials under US sanctions, but State Department spokesperson Heather Nauert said she was sure that the US had taken appropriate administrative steps to allow him to visit New York unmolested.
His journey to the US caps a frenetic few days of meetings between North Korean and American officials.
Japanese broadcaster NHK showed footage of Kim Chang Son, Kim Jong Un's de facto chief of staff, arriving in Singapore, escorted by three bodyguards.
An AFP photographer saw Kim entering Singapore's luxury Fullerton hotel Tuesday and leaving some 30 minutes later in a three-vehicle convoy.
Diplomatic duels: what now for the Trump-Kim summit?
If the June 12th date stands, officials have only two weeks to finalise details such as where in Singapore the talks will take place and how internationally sanctioned North Korean officials will travel there.
The key task is to settle the agenda. The main stumbling block is likely to be the concept of 'denuclearisation' - both sides say they want it, but there is a yawning gap between their definitions.
Washington wants North Korea to quickly give up all its nuclear weapons in a verifiable way in return for sanctions and economic relief.
But analysts say North Korea will be unwilling to cede its nuclear deterrent unless it is given security guarantees that the US will not try to topple the regime.
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