SEOUL, South Korea -- President Trump and Secretary of State Mike Pompeo appear to be on different pages about when the U.S. might start to peel back sanctions against North Korea. Mr. Trump said on Tuesday, immediately after his summit with Kim Jong Un, that sanctions would be rolled back when the North's nuclear weapons are no longer a factor, and indicated that could happen when the denuclearization process is 20 percent complete.

Pompeo, on the other hand, continues to reiterate the long-held administration policy that sanctions will not be rolled back until denuclearization is complete.

"The sanctions will come off when we are sure that the nukes are no longer a factor. Sanctions played a big role, but they'll come off at that point. I hope it's gonna be soon," Mr. Trump told reporters in Singapore after his meeting with Kim.

"Scientifically you have to wait certain amount of time. And a lot of things happen. But despite that, once you start the process it means it's pretty much over -- you can't use them. That's the good news. And that's going to start very, very soon, I believe that's going to start very soon," said Mr. Trump.

He explained that he had spoken with nuclear experts and believes that when the denuclearization process is "20 percent through," North Korea will be at a point where it "can't go back."

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Experts have told CBS News that complete denuclearization could take anywhere between three and 15 years. Neither Mr. Trump nor any experts or other members of his administration have mentioned the 20 percent threshold since his Tuesday news conference, and it remains unclear how long it could take to reach that stage in the process, or what major steps would constitute it.

The Trump administration has been vocal about its desire to speed up the denuclearization process. Pompeo said Thursday that the White House is looking for "major disarmament" within Mr. Trump's first term, which leaves two and a half years.

Pompeo, speaking in South Korea after the summit, wouldn't budge on the possibility of sanctions coming off in phases, as both Mr. Trump and the North Koreans have suggested.

"We are going to get complete denuclearization, only then will there be relief from the sanctions," Pompeo said Thursday. "But they'll come off -- as you know, and as I've said, sanctions right now remain. But at a certain point, I actually look forward to taking them off. And they'll come off when we know we're down the road."

The North Koreans seem to be in closer lockstep with President Trump than the president's own Secretary of State. After the summit, North Korea's state-run media indicated that Mr. Trump would grant concessions before Pyongyang completes the denuclearization process.

The joint document signed by both leaders at the Trump-Kim summit does not lay out a concrete path for denuclearization or the lifting of sanctions. In the four-point joint statement, North Korea committed only "to work toward complete denuclearization of the Korean Peninsula." Kim's predecessors -- his father and grandfather -- made that promise several times, but never kept it.

Pompeo said the U.S. would work with its allies, namely South Korea and Japan, to implement the process as "quick and as complete" as possible.

He suggested that he hoped a framework for the process could be worked out, "over the coming days and weeks."

That may be a lofty goal, given that the U.S. negotiating teams left their conversations with North Korean counterparts without bridging major differences over how or when denuclearization might actually happen.

The Trump administration has been adamant that U.S. inspectors must be on the ground, alongside scientists from other countries, to ensure North Korea is following through on its pledge to denuclearize.

Right now, North Korea has the most advanced nuclear program and missile arsenal in its history. Experts say the North has enough material to make 25-30 nuclear weapons. Their intercontinental ballistic missiles have the range to hit the U.S. mainland, though there are still major questions about their accuracy and ability to deliver an in-tact warhead.

Before taking office people were assuming that we were going to War with North Korea. President Obama said that North Korea was our biggest and most dangerous problem. No longer - sleep well tonight! — Donald J. Trump (@realDonaldTrump) June 13, 2018

Nevertheless, Mr. Trump tweeted on Wednesday, before the denuclearization process even begins, that Americans should "sleep well," because, in his words, North Korea was "no longer" the United States' "biggest and most dangerous problem."