Iran itself cautioned North Korea against taking Trump at his word.
The head-scratching was a fitting end for a meeting marked by unpredictability.
While the Singapore sit-down at a luxury resort purported to be a serious conversation about a rising nuclear standoff, it was as much an opportunity for two decidedly unorthodox leaders to put on a show.
Earlier Wednesday, Trump wrote online that North Korea no longer poses a nuclear threat to the USA after his meeting this week in Singapore with Kim, adding that Americans should "sleep well tonight". Tammy Duckworth (Ill.) and Chris MurphyChristopher (Chris) Scott MurphyDemocrats seize on DOJ's ObamaCare decision ahead of midterms Navarro apologizes for saying there's a "special place in hell" for Trudeau Dems rip Trump concessions, "embarrassing" rhetoric with Kim MORE (Conn.) said in a joint statement.
He gave Mr Kim a glimpse of the presidential limousine.
The president called his meeting with Kim "honest, direct and productive", and said Pyongyang promised to a "major missile site" though this was agreed after the deal was signed, explaining its absence from the document.
There was shock, relief, worry, sometimes simultaneously, as the world watched Trump and Kim - who were insulting each other's mental and physical prowess and threatening nuclear war just a few months ago - shaking hands and smiling.
"I think it's gonna be really successful, and I think we will have a terrific relationship, I have no doubt", Trump said. The details of how and when the North would denuclearize appear yet to be determined, as are the nature of the unspecified "protections" Trump is pledging to Kim and his government.
Experts believe the North is close to being able to target the entire USA mainland with its nuclear-armed missiles, and while there's deep skepticism that Kim will quickly give up those hard-won nukes, there's also some hope that diplomacy can replace the animosity between the US and the North.
In Trump's case, he has just two and a half years remaining in his first presidential term.
The announcement caught not only allies Japan and South Korea off guard, it also took the U.S. military command in the South, U.S. Forces Korea, by surprise.
Korea no longer nuclear threat, tells Americans to "sleep well"
Still, others might say let's wait until there's an actual peace deal before we start doling out the accolades. Secretary of State Mike Pompeo arrived at Osan Air Base south of Seoul from Singapore early Wednesday evening.
"We're going to have a great discussion, and I think tremendous success", Trump said alongside Kim, according to Yonhap News Agency.
It may not have been the focus of the summit, but Korean War vets and their families were hoping the issue would come up.
Earlier in the day, Trump declared that there is 'no longer a nuclear threat from North Korea'. The length of the contact, their facial expressions and body language, the stunning backdrop of interlocked national flags - all of it was instantly analyzed, criticized and marveled at in tweets and commentary in South Korea, the United States and beyond.
US Forces Korea said in a statement on Tuesday it was unaware of any policy change.
Pompeo will meet South Korean President Moon Jae-in on Thursday morning to discuss the summit.
Secretary of State Mike Pompeo flew to Seoul on Wednesday for follow-up meetings.
South Korean Minister of Defence, Itsunori Onodera, said: "We would like to seek an understanding of this between Japan, the US and South Korea".
The Pentagon said Tuesday it was consulting with the White House and others, but was silent on whether the August exercise would proceed. Mr Pence's spokeswoman later denied that comment.
Trump has said he'll know within minutes whether a deal can be made to settle a standoff over Pyongyang's nuclear program.
Trump's Tuesday meeting with Kim produced a wave of U.S. concessions in exchange for vague, nonbinding promises from North Korea, but it did make nuclear war all but inconceivable at the present moment.
A wise move, Mr Broinowski said, "this had to be nuclear".