National security adviser John Bolton, meanwhile, said that the North's nuclear and ballistic missile programs could be dismantled within a year - a timeline that stands in contrast with the conclusions of many experts who say it would take several years even under the best of circumstances.
After visiting the North Korean capital later this week, the State Department said Monday that Pompeo will travel to Japan, Vietnam and the United Arab Emirates before heading to Belgium, where he will accompany President Donald Trump at the NATO summit in Brussels.
In a sign the two sides are stepping up diplomacy, the USA ambassador to the Philippines, Sung Kim, led a delegation to the tense border area on Sunday in the highest-level meeting with the North since the June 12 summit.
The Post said the evidence of North Korean cheating had emerged since the June 12 summit, where Kim and Trump signed a pledge "to work towards complete denuclearization of the Korean Peninsula".
- North Korea will be just the first stop on Secretary of State Mike Pompeo's first around-the-world trip as America's top diplomat.
According to the daily, evidence collected by U.S. intelligence points to preparations to deceive the United States about the number of nuclear warheads in North Korea's arsenal as well as the existence of undisclosed facilities used to make fissile material for nuclear bombs.
North Korea and Washington have yet to negotiate the terms under which the North would relinquish its weapons, so Pyongyang can be expected to seek leverage in those discussions. In reality, the document Kim signed contained language that had already been agreed to in previous treaties, under which the North Korea's nuclear program continued unabated.
Victor Cha, the Korea Chair at the Center for Strategic and International Studies, also told Axios that the Trump administration "needs to get a commitment to a full declaration" and have international experts in North Korea "sealing stuff and installing cameras" to ensure North Korea sticks to its promises.
But reports that North Korea intends to secretly maintain some of its nuclear stockpile and production facilities raised questions Sunday.
Bolton, who has expressed hard-line views on North Korea, said that if Pyongyang has made a decision to give up its nuclear weapons program and is cooperative, then "we can move very quickly" and they can win sanctions relief and aid from South Korea and Japan.
The statement said Pompeo and "relevant high-level" North officials will hold follow-up negotiations "at the earliest possible date" to implement the outcomes of the summit.
In a subsequent appearance on Fox News Sunday, Bolton refused to comment on the Washington Post report. North Korea has great potential for the future! The country appears to be ramping up production of both nuclear fuel and ballistic missile components, according to multiple reports.
"Now we're saving a lot of money", Trump said of the cancellation of large-scale military drills that involve flights of U.S. bombers from the Pacific U.S. territory of Guam. She declined to confirm or deny recent media reports of intelligence assessments saying North Korea has been expanding its weapons capabilities.