"But lots of other places where there were understandings reached, we couldn't reduce them to writing, so that means there's still some work to do, but there was a great deal of work done that is beyond what was seen in the final document that will be the place that we will begin when we return to our conversations", Pompeo said after flying to Seoul from Singapore.
The president planned to stop in Guam and Hawaii on his way back to Washington. Trump then directed Kim to walk down a hallway, where they briefly spoke.
He joined Singapore's foreign minister, Vivian Balakrishnan, who tweeted a selfie with a smiling Kim and Singapore Education Minister Ong Ye Kung, against a backdrop of flowers with the hashtag #Guesswhere.
Outside the Korean community, local peace groups called for the USA government to allow North and South Korea to negotiate a deal for peace on their own.
It was a striking about-face from less than a year ago, when Trump was threatening "fire and fury" against Kim, who in turn scorned the American president as a "mentally deranged United States dotard". Many have been quick to point out that it isn't the best look for Singapore's Balakrishnan to be seen grinning alongside a man who just 16 months earlier had ordered his half-brother killed in an attack at Kuala Lumpur International Airport, some 200 miles north of Marina Bay Sands in Singapore. Or, it could amount to little more than a much-photographed handshake.
Kim's main concern is the survival of his own regime - South Korean President Moon Jae-in told reporters that the Pyongyang leader had "concerns on whether he could trust that the U.S. would end its hostile policy and guarantee the security of his regime when the North denuclearises itself". Raising human rights risks playing into North Korean suspicions that the U.S is intent on toppling its hereditary, totalitarian regime by seeking to open its political system, which only reinforces Pyongyang's notion that it needs a nuclear deterrent to ensure its survival.
On Monday morning, the KCNA and the Rodong Sinmun, the official newspaper of the North's ruling party, gave extensive reports on Kim's departure for Singapore and his meetings with Singaporean officials, including its Prime Minister Lee Hsien Loong. It was an extraordinarily compressed timeline for the landmark summit, one that left aides scrambling to initiate communication with the hermit nation.
"China might have wanted to prevent Chinese smugglers from entering North Korea so they cracked down on smuggling organizations in the border area few days ago and arrested number of smugglers", he said.
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But after a flurry of diplomatic overtures eased tension in recent months, the two leaders are now headed for a history-making handshake that USA officials hope could eventually lead to the dismantling of a North Korean nuclear programme that threatens the United States.
Trump advisers cast his actions as a show of strength before the Kim meeting.
He said secretary of state Mike Pompeo and defence secretary Jim Mattis should have opposed the one-on-one meeting "in writing" - and called for the national security council to have a transcript of all interactions with the "brutal, nuclear armed dictator".
The North has faced crippling diplomatic and economic sanctions as it has advanced development of its nuclear and ballistic missile programs.
Experts believe the North is close to being able to target the entire USA mainland with its nuclear-armed missiles, and while there's deep skepticism that Kim will quickly give up those hard-won nukes, there is also some hope that diplomacy can replace the animosity between the U.S. and the North.
Kim told reporters he was able to overcome obstacles to make his way to the Singapore summit.
"I think of myself as American", he said. "That's what I do".