The official was not authorized to speak publicly about internal deliberations and insisted on anonymity.
After greeting each other for the first time Tuesday in front of reporters, the American president and the North Korean leader will seclude themselves on Singapore's Sentosa Island for roughly 45 minutes, while their entourages wait nearby.
The White House said on Monday ahead of the scheduled talks that the meeting between the two leaders, which will focus largely on North Korea's possible denuclearization, has moved "more quickly than expected". Yet even before they met, Trump announced plans to leave early, raising questions about whether his aspirations for an ambitious outcome had been scaled back.
While the two leaders are hoping to hammer out the framework of a denuclearisation deal for the Korean peninsula, the U.S. and North Korea have yet to agree on what exactly denuclearisation would entail. Mr Kim is reported to be flying out even earlier, at 14:00 local time (6pm NZT).
The North Korean leader has also said he now wants to focus on building the country's economy - and wants sanctions relief and global investment.
Despite the initial high stakes of a meeting meant to rid North Korea of its nuclear weapons, the talks have been portrayed by Trump in recent days more as a get-to-know meeting.
In a statement obtained by CNN, Rodman says he considers Trump to be a friend and expressed his confidence in his ability to get the job done in their summit.
"I have every expectation that they will continue to do that", he said. He told reporters he thinks he will know nearly immediately whether a deal can be made, saying: "I will know, just my touch, my feel".
Pompeo added, President Trump is very prepared for his upcoming meeting with Kim Jong Un and is eager to achieve real progress.
Pompeo, who shifted to his current role in the spring after serving as Trump's Central Intelligence Agency director, spent Monday morning preparing with his top advisers, aides said.
The trip to Singapore - nearly 3,000 miles (5,000 kilometers) south of Pyongyang - represents Kim's farthest trip from home since taking power after his father's death in 2011.
A man in Seoul, South Korea, watches news footage of a North Korean missile launch in May 2016. On a larger level, the astronomical cost of the nuclear weapons program contributes to the massive poverty in North Korea, among the world's poorest countries.
"The irony ... is that what was initially presented as a cliff-hanger dramatic summit, upon which war or peace on the Korean peninsula hung is now looking more like conventional diplomacy for the unconventional Trump White House", Cha told a Senate Foreign Relations subcommittee last week.