Secretary of State Mike Pompeo reportedly is preparing for his third trip to North Korea later this week to discuss a proposed timeline for full denuclearization of the Korean peninsula. He meets with President Trump today.

Washington and Pyongyang have yet to negotiate a plan for how North Korea will denuclearize. And as for a timeframe, while National Security Adviser John Bolton says it will happen within a year, Pompeo says that timeline is closer to two-and-a-half years, reports CBS News correspondent Paula Reid.

President Donald Trump and Kim Jong Un during their summit in Singapore June 12, 2018. Reports suggest the North Korean leader is continuing with his nuclear program despite the president claiming, "There is no longer a nuclear threat." JONATHAN ERNST/REUTERS

President Donald Trump told Fox News Sunday he trusted Kim Jong Un would dismantle his nuclear program ("I made a deal with him"), but admitted the deal they agreed to in Singapore last month could fall apart.

"Have I been in deals, have you been in things where, people didn't work out? It's possible," he said.

That's far from Mr. Trump's confident tone arriving home from the summit, when he tweeted, "There is no longer a nuclear threat."

But new satellite imagery shows an expansion of a missile-manufacturing site capable of producing missiles that could hit U.S. military installations in Asia.

The North Koreans were finishing construction of the plant around the same time President Trump was meeting Kim in Singapore.

"It goes to show the intentions and expectations that the North Koreans had going into the meeting," said David Schmerler, a researcher at the Middlebury Institute of International Studies at Monterey. "It shows that they are fully committed to maintaining their ballistic missile program."

This comes on top of a Washington Post report that U.S. intelligence believes the North Koreans are planning to conceal the number of warheads in their arsenal.

On Sunday's "Face the Nation," Bolton would not address the Washington Post article, arguing the administration had a plan to fully dismantle their nuclear program.

"I don't want to comment on that specific report," Bolton said. "We have developed a program. I'm sure that Secretary of State Mike Pompeo will be discussing this with the North Koreans in the near future about really how to dismantle all of their WMD and ballistic missile programs in a year."

Behind the scenes, the diplomacy continues. Over the weekend, a U.S. envoy met with the North Koreans at the DMZ.

Bolton also said the administration's plan would require the North Koreans to provide full disclosure of all their nuclear programs and ballistic missile sites, but that has not happened yet.