North Korea's leader Kim Jong Un (L) shakes hands with US President Donald Trump (R) at the start of their historic US-North Korea summit, at the Capella Hotel on Sentosa island in Singapore on June 12, 2018.

President Donald Trump has received what the White House said is a "very warm, very positive letter" from North Korean leader Kim Jong Un, requesting a follow-up meeting with Trump after the summit in Singapore earlier this year.

"The primary purpose of the letter was to request and look to schedule another meeting with the president," White House press secretary Sarah Huckabee Sanders told reporters at the press briefing Monday. It was a request, she said, "which we are open to and already in the process of coordinating."

Talk of another Trump-Kim meeting initially seemed like an about-face for Trump, following the president's abrupt decision in late August to cancel a planned trip to North Korea by Secretary of State Mike Pompeo.

At the time, Trump tweeted, "I have asked Secretary of State Mike Pompeo not to go to North Korea, at this time, because I feel we are not making sufficient progress with respect to the denuclearization of the Korean Peninsula."

Asked by reporters on Monday what had changed in the three weeks since Trump canceled Pompeo's trip, Sanders cited a recent parade in Pyongyang. The annual parade has traditionally featured a display of intercontinental ballistic missiles, an obvious nod to North Korea's nuclear weapons program. This year, however, there were reportedly no ICBMs at the parade.

"The recent parade in North Korea, for once, was not about their nuclear arsenal," Sanders said, adding that the letter from Kim was "further evidence of progress" in the Trump administration's goal of denuclearizing the Korean Peninsula.

But there are still serious issues standing in the way of further progress on North Korea. Notably, a new report from NBC News on Monday featured an assessment from intelligence officials that Kim is indeed still making nuclear weapons.

Citing U.S. intelligence officials, NBC also reported that North Korea is escalating its efforts to hide certain nuclear facilities, possibly to keep satellite images from revealing activity taking place there. The country is also moving nuclear warheads between various facilities, according to the officials.

The hardening intelligence assessment comes less than three months after Trump held a historic summit with Kim in Singapore in June, after which the president tweeted, "There is no longer a Nuclear Threat from North Korea."

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