US President Donald Trump says his historic talks with North Korean leader Kim Jong-un that ended in a joint agreement were "tremendous".
But in an extraordinary media conference later, Mr Trump announced details not in the document.
The signed document includes a pledge from Mr Kim to rid the Korean peninsula of nuclear weapons.
Mr Trump later said he would halt US military exercises in South Korea, something widely seen as a concession.
The declaration took some South Korean and US military officials by surprise - though US Defence secretary Jim Mattis was not among them, with spokeswoman Dana White saying "there were no surprises".
If implemented, the halting of the joint military exercises would be one of the most controversial moves to come from the summit. The drills help keep US forces at a state of readiness in one of the world's most tense flashpoints.
"We will be stopping the war games which will save us a tremendous amount of money, unless and until we see the future negotiation is not going along like it should. But we'll be saving a tremendous amount of money, plus I think it's very provocative," Mr Trump said.
His announcement was a surprise even to President Moon Jae-in's government in Seoul, which worked in recent months to help bring about the Trump-Kim summit.
The presidential Blue House said it needed "to find out the precise meaning or intentions" of Mr Trump's statement, while adding that it was willing to "explore various measures to help the talks move forward more smoothly".
Pentagon officials were not immediately able to provide any details about Mr Trump's remarks on suspending drills, something that the US military has long resisted.
A spokeswoman for US military forces in Korea said it had not received any direction to cease joint military drills.
Current and former US defence officials expressed concern at the possibility that the United States would unilaterally halt military exercises without an explicit concession from North Korea that lowers the threat from Pyongyang.
The meeting was the first time a sitting US president has met North Korea's leader.
The agreement said the two countries would co-operate towards "new relations", while the US would provide "security guarantees" to North Korea.
On nuclear weapons, Mr Kim "reaffirmed his firm and unwavering commitment to complete denuclearisation of the Korean peninsula".
Observers say the document lacks substance, in particular on how denuclearisation would be achieved.
However, speaking to reporters after, Mr Trump said:
- The US would suspend "provocative" war games it holds with South Korea. Mr Trump said he wanted to see US troops withdraw from the South. A spokesperson for the US forces said they had yet to receive any new guidance
- On denuclearisation, he said that Mr Kim had agreed to it being "verified", a key US demand ahead of the meeting
- Mr Trump said Mr Kim had also agreed to destroy a "major missile engine testing site"
- But he said sanctions would remain in place for now and argued "we haven't given up anything"
Several reporters asked whether Mr Trump had raised the issue of human rights with Mr Kim, who runs a totalitarian regime with extreme censorship and forced-labour camps.
The US president said he had, and did not retract his description of Mr Kim as "talented".
"Well, he is very talented," Mr Trump said. "Anybody that takes over a situation like he did at 26 years of age and is able to run it and run it tough. I don't say he was nice."
In a post-summit interview with ABC News, the president said he was confident that the agreement meant full denuclearisation.
"Yeah, he's de-nuking, I mean he's de-nuking the whole place. It's going to start very quickly. I think he's going to start now," he said.
- BBC / Reuters