Speaking to US media, CIA director Mike Pompeo defended US President Donald Trump's decision to meet with the leader, portraying North Korea as buckling under the pressure of US-led international sanctions, and insisted there would be no let-up for the duration of the negotiations.
"Never before have we had the North Koreans in a position where their economy was at such risk, where their leadership was under such pressure," he said on Fox News Sunday.
"Make no mistake, while these negotiations are going on, there will be no concessions made," he said
While key details of the summit are yet to be decided, South Korean media is reporting North Korea wants to sign a peace treaty with the US following the talks.
The Sunday talk show appearances by Pompeo and others served to answer critics who warn that the talks, entered into by an impulsive, inexperienced president, carry high risks.
If they fail, the two nuclear-armed states could then be left with few options short of military confrontation, experts on the years-long impasse with North Korea say.
Pompeo suggested that Trump understood the dangers. "The president isn’t doing this for theatre, he is going there to solve a problem."
Trump used a Saturday night campaign rally in Pennsylvania steel country to defend his decision to sit down with Kim after months of insult-filled brinkmanship, replete with nuclear threats.
He said the United States had "shown great strength" when tensions were high but the regime's leaders "want to make peace."
"I think it's time," Trump told supporters.
Before boarding his Marine One helicopter for the rally, he told reporters: "I think North Korea is going to go very well, I think we will have tremendous success... We have a lot of support."
"The promise is they wouldn't be shooting off missiles in the meantime, and they're looking to de-nuke. So that'd be great."
What next?
Trump accepted the invitation Thursday after it was relayed to him in an impromptu White House meeting with the South Korean national security adviser, Chung Eui-yong.
Chung, who had met with Kim previously, told Trump that the North Korean leader had pledged to halt missile and nuclear tests during the negotiations, to discuss denuclearization and to raise no public objections to scheduled US-South Korean military exercises.
What comes next is unclear.
Deputy press secretary Raj Shah would not rule out a White House summit or Trump going to North Korea for the talks, although he said on ABC's "This Week" that the latter venue was not "highly likely."
Pompeo said "channels are open" but he shed no light on how the United States will proceed or even whether it has heard back from the North Koreans on Trump's agreement to talk to Kim.
Two key Trump advisers were out of the country, US Secretary of State Rex Tillerson being in Africa and Defense Secretary Jim Mattis in Oman.
Neither Tillerson, Mattis nor National Security Adviser H.R. McMaster has commented substantively on the North Korea talks.
'Potential for misunderstanding'
"I do not want to talk about Korea at all. I will leave it to those who are leading the effort," Mattis told reporters during a flight to Oman, "because it’s that delicate when you get into a position like this."
"The potential for misunderstanding remains very high or goes higher."
Pompeo said there wasn't "any doubt about who is going to take the lead on this."
"The president of the United States is going to take the lead," he said on CBS's "Face the Nation".
Trump reached out to the leaders of China and Japan in phone calls Friday, and later said he had received encouragement for the diplomatic gambit.
He tweeted that Chinese President Xi Jinping "appreciates that the US is working to solve the problem diplomatically rather than going with the ominous alternative. China continues to be helpful!"
He described Japan's Prime Minister Shinzo Abe as "very enthusiastic."
A White House readout of the conversation with Xi said the two leaders committed to keeping the pressure on North Korea until it takes "tangible steps toward complete, verifiable and irreversible denuclearization."
Potentially explosive
Not everyone was so sanguine about the prospects of a breakthrough, however, and some Democrats shuddered at the thought of such sensitive - and potentially explosive - negotiations being in Trump's hands.
"I am very worried that he's going into these negotiations and be taken advantage of," Senator Elizabeth Warren, a leading liberal voice, said on CNN.
She said that while diplomacy was good, the State Department has been "decimated" with no US ambassador in South Korea or an assistant secretary for the region.
Republican Senator Jeff Flake of Arizona was skeptical that North Korea would abandon its nuclear weapons.
"I don’t think anybody really believes that North Korea is prepared to denuclearize," he said on NBC's "Meet the Press."
"Now, maybe a freeze where they say, ‘All right. We are a nuclear power. Let’s get some security guarantees.’ But denuclearization, [as] I’ve heard it suggested, that that’s what the North Koreans have already agreed to, I would question that."
