Newly minted U.S. Secretary of State Mike Pompeo said Sunday he has spoken with North Korean leader Kim Jong Un about how the isolated country might relinquish its nuclear arsenal and what a “complete, verifiable, irreversible mechanism might look like.”

Asked on ABC News’ “This Week” about his clandestine visit to Pyongyang over Easter weekend to lay the groundwork for U.S. President Donald Trump’s planned meeting with Kim, Pompeo, who prior to being sworn in as the top U.S. diplomat on Thursday had been serving as CIA chief, called the trip a “productive one,” adding that there is “a real opportunity” for the two leaders to strike a deal.

Pompeo, in his most extensive comments yet on the secret meeting with Kim, said the two had discussed a number of issues that could be achieved at the summit.

“I talked about getting the release of the American detainees, and then we talked a great deal about what it might look like, what this complete, verifiable, irreversible mechanism might look like,” Pompeo said.

North Korea continues to hold three U.S. citizens in the wake of the death last June of American college student Otto Warmbier, who died shortly after being released and repatriated from 17 months in a North Korean prison.

Pompeo did not elaborate on what a denuclearization “mechanism” might look like, but Kim reportedly asked Pompeo to agree to a “phased” approach, a proposal that would likely take years to realize.

The Trump administration, however, is wary of agreeing to that, and instead is pushing for a “big bang” approach involving major concessions at an early juncture, The Wall Street Journal reported last week.

Pyongyang conducted its sixth and most powerful nuclear test last year and launched more than 20 missiles — including two intermediate-range weapons that flew over Japan and another long-range missile that experts say puts the whole of the United States within striking distance. With the test of that long-range missile in November, the North said it had “realized the great historic cause of completing the state nuclear force.”

The North has made building up its nuclear weapons program a top priority despite a punishing sanctions regime that has grown increasingly stringent under Trump’s “maximum pressure” campaign.

Asked if the administration might loosen sanctions or reward the Kim regime before the total, irreversible dismantling of its nuclear program, Pompeo was circumspect.

“This administration has its eyes wide open,” he said. “We know the history; we know the risks. We’re going to be very different. We’re going to negotiate in a different way than has been done before. We’re going to require those steps.”

Kim, he said, would have to agree to take “irreversible” steps toward dismantling its nuclear weapons program in any deal.

“We use the word ‘irreversible’ with great intention. We are going to require those steps that demonstrate that denuclearization is going to be achieved,” Pompeo said, adding that the pressure campaign would remain in place “until we achieve that.”

Pompeo said Kim is going to have to make “a big decision” about his nuclear weapons and his own future.

“Does he want the pressure campaign to continue?” he asked. “Does he want President Trump to continue to place him in the location that he finds himself today? Or is he looking for something big and bold and different, something that hasn’t happened before?”

Pompeo’s meeting with Kim, which Trump said Thursday had not been planned, comes as planning for the U.S. president’s summit with the North Korean leader ramps up. Trump told a rally Saturday that the meeting would likely be held within three to four weeks and that the location had been narrowed down to two sites.

National security adviser John Bolton, making his first Sunday show appearances since assuming that role in March, told “Fox News Sunday” that the president is eager to hold the meeting “as soon as possible.”

Bolton also said that the administration was eying Libya’s decision to give up its nuclear program through diplomacy in exchange for being allowed to join the international community as a model for the North Korean efforts.

“We have very much in mind the Libya model from 2003, 2004,” Bolton told “Fox News Sunday” when asked if North Korea would have to fully give up its nuclear weapons, fuel and missiles before the U.S. makes concessions.

“There are obviously differences; the Libyan program was much smaller. But that was basically the agreement that we made,” Bolton said.

“We’ll want to test North Korea in this first meeting for evidence that they have made this strategic decision” to end its program, he said.

Libya’s move to scrap its program, however, also serves as an example of what the Kim regime fears most — its government, then led by Moammar Gadhafi, was later overthrown by rebel forces supported by Western airstrikes. When he was eventually caught by rebels, Gadhafi suffered the ignominious fate of being brutally beaten, sodomized with a bayonet and then shot dead.

The North regularly cites the fates of Gadhafi and Saddam Hussein in Iraq — whose government was toppled in a U.S.-led invasion and who was later executed — as evidence of the need for a nuclear deterrent.

“Pyongyang has long been wary of proposed U.S. security guarantees,” said Abraham Denmark, a former Asia official at the Pentagon who is now with the Wilson Center think tank in Washington. “This goes back to past collapsed agreements, and North Koreans often point to Gadhafi and Saddam Hussein as examples of what happens to countries that trade away their nuclear programs.”

The White House has consistently said that “all options” — including military action — remain on the table for dealing with the nuclear crisis. And while the Trump administration’s threats of military strikes have waned amid easing tensions on the Korean Peninsula, allusions to that possibility have continued.

“We’re not going to allow Kim Jong Un to continue to threaten America,” Pompeo said Sunday. “We’re not going to let him develop a program such that Americans are held at risk.”