"It's clear that the North Koreans feel the White House doesn't get it," said Jean Lee, the director of the Hyundai Motor-Korea Foundation Center for Korean History and Public Policy at the Wilson Center.

'Political dummy'

"There was some talk about the Libya model," Pence told Fox News' Martha MacCallum. "As the President made clear, this will only end like the Libya model ended if Kim Jong Un doesn't make a deal."

When MacCallum said that some people may have seen Bolton's comments as a threat, Pence said "I think it's more of a fact."

North Korea has long cited Libya's case as the reason it needs nuclear weapons. Less than a decade after Moammar Gadhafi agreed to abandon its nuclear aspirations in a deal with the United States, he was ousted from power and killed with the help of NATO-backed forces.

"They (the North Koreans) are very proud, they don't like being bullied and they certainly don't like the repeated references to Libya and the repeated reference to its poverty," Lee said.

Adam Mount, the director of the Defense Posture Project at the Federation of American Scientists, believes Pence's comments were the "most explicit regime change threat yet" from the Trump administration.

"The Libya analogy is deliberately inflammatory. It never applied to North Korea and is useful neither to convey resolve or to set expectations on nuclear issues," he told CNN in an email.

Choe called Pence a "political dummy" for comparing Libya to North Korea. She noted that Libya's nuclear program was in its early stages when it came to the negotiating table, while North Korea has spent years developing its nuclear weapons.

"As a person involved in the US affairs, I cannot suppress my surprise at such ignorant and stupid remarks gushing out from the mouth of the US vice president," she said.

Pence has been vocal critic of North Korea and its human rights abuses.

While representing the United States at the Winter Olympics in South Korea earlier this year, he brought along the father of Otto Warmbier, an American university student who was imprisoned in North Korea and died shortly after his return to the United States in a vegetative state. At the opening ceremony, he chose to ignore Kim Yo Jong, Kim Jong Un's sister, when sitting feet away from her.

Analysts believe that Choe, a diplomat who focuses on the US-North Korea relationship, is a rising star in North Korea's Foreign Ministry. She was reportedly promoted to vice minister earlier this year.

Summit preparations underway

Speaking alongside his Chinese and Japanese counterparts in Washington, US Secretary of State Mike Pompeo told reporters he's hopeful about the prospects.

"I hope that we can have this opportunity, this historic opportunity to do something that would truly transform this global challenge that's been threatening the world for an awfully long time," he said.

The White House has maintained it will not repeat what it believes were mistakes by previous US administrations -- signing on to agreements that were supposed to exchange concessions for steps toward denuclearization over time.

But some experts worry about that approach, and it's unclear if the North Koreans would be interested.

"Pyongyang is trying to shift the discussion away from immediate disarmament and economic benefits and toward a protracted exchange of security concessions," said Mount of the Federation of American Scientists.

"Dismantling a weapons program this complex would take time to fully understand and safely tear down. It is not reasonable or prudent to rush this process."