But Mr Trump dismissed suggestions that he had been premature in his declarations of success, tweeting: "In the meantime, no Rocket Launches or Nuclear Testing in 8 months".
"What it suggests is that Kim has no intention of surrendering his nuclear weapons".
US intelligence agencies believe North Korea has increased production of fuel for nuclear weapons at multiple secret sites in recent months and may try to hide these while seeking concessions in nuclear talks with the United States, NBC News quoted USA officials as saying on Friday.
The U.S. State Department said here Tuesday it will not provide a timeline for the abandonment of nuclear and missile program of the Democratic People's Republic of Korea (DPRK).
North Korea's deputy sports minister, Won Kil U, led the North's welcoming party.
USA officials caution Kim would have to show progress in denuclearizing before a meeting could be arranged.
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On CBS's "Face the Nation," Bolton said North Korea's nuclear arsenal could be dismantled in a year if Pyongyang cooperates, adding that the program would require "full disclosure of all [of North Korea's] chemical and biological, nuclear programs, ballistic missile sites".
"I think they want to do it".
A spokesman for South Korean President Moon Jae-in told reporters it's "inappropriate" to comment on reports suggesting North Korea has not stopped construction at weapons facilities and intelligence matters on the whole.
National Security Adviser John Bolton said the USA could dismantle the regime's stockpile in a year if Kim would cooperate.
"In terms of a timeline, I know some individuals have given timelines", said Heather Nauert, the spokeswoman of the State Department at a press briefing Tuesday, apparently referring to Bolton, the US national security adviser.
This source said that they are unaware of any new projects the North Koreans may be working on, but reiterated that "they have given nothing up".
Van Jackson, a former Pentagon official who now teaches at Victoria University in New Zealand, said that the presence of a respected diplomat like Sung Kim could level the playing field during negotiations with North Korea, adding that Pompeo was using the "best folks he can find in the bureaucracy".
"There's not any starry-eyed feeling among the group doing this", he said.
Speaking to Fox, Trump also sought to shrink the perceived cost of the declared agreement falling through, seeking to frame his negotiations with North Korea as having been achieved without concessions. Collins stressed the need for "verifiable, unimpeded, reliable inspections" of the North's weapons programs.