The US has offered North Korea "unique" security guarantees to persuade it to give up its nuclear arsenal, Secretary of State Mike Pompeo said Monday, on the eve of a historic summit in Singapore.
The White House said preparatory negotiations had "moved more quickly than expected" and Donald Trump would leave Tuesday evening after his talks with Kim Jong Un, ruling out the possibility the unprecedented tete-a-tete would run to two days.
The meeting, long sought by Pyongyang, will be the first ever between a serving US president and a North Korean leader, and will focus on the nuclear bombs and ballistic missiles the North has spent decades developing.
Just hours ahead of the crunch talks, Kim left his luxury hotel for a night-time stroll around some of Singapore's main sights, even posing for selfies with his guide, the city-state's foreign minister.
Setting out the US position before the summit, Pompeo stressed that the Trump administration would only accept complete denuclearisation of the North.
But in return, Washington would offer "different and unique" guarantees "to provide them sufficient certainty that they can be comfortable that denuclearisation is not something that ends badly for them".
He refused to go into details. But the North has long sought an end to the US military presence in the South, where Washington has around 28,000 troops stationed to protect it from its neighbour.
Pyongyang has demanded the end of what it calls a "hostile policy" towards it, but in public has only pledged to pursue the denuclearisation of the Korean peninsula -- a euphemism open to wide differences of interpretation.
Washington is eager to see if the North's pledges were "sincere", Pompeo said, adding: "The United States has been fooled before."
Verification would be key, he went on, saying many deals had been signed before only to find "the North Koreans did not promise what they said".
The North, which has been subjected to increasingly strict sanctions by the UN Security Council and others, has made promises of change in the past, such as at the lengthy Six Party Talks process, only for the agreements to collapse later.
Trump and Kim will first meet one-on-one in a closed session, before a larger meeting with key advisers, the White House said.
The wider session will include National Security Advisor John Bolton, who nearly derailed the summit with hawkish comments about disarming North Korea.
Pompeo also signalled there would be more discussions to come, adding that Tuesday's meeting "will set the framework for the hard work that will follow. We will see how far we get."
In Seoul, President Moon Jae-in had a 40-minute phone call with Trump, after telling key aides that it could take "one year, two years or even longer to completely resolve the issues concerned".
Tuesday's summit is an extraordinary turnaround from last year, when Trump threatened the North with "fire and fury" and Kim dubbed him a "mentally deranged US dotard", sending fears of conflict soaring.
The summit has also raised hopes of progress towards a peace treaty to formally end the Korean War, the last festering legacy of the Cold War, after hostilities only stopped with an armistice.
But critics have warned it risks becoming more of a media circus than an occasion for substantial progress.
The US leader has whipsawed on expectations for the meeting, signalling that it could be the beginning of a "process" of several meetings, only to call it a "one-time shot" for peace as he embarked for Singapore and saying he would know "within the first minute" whether an agreement would be possible.
"I just think it's going to work out very nicely," said Trump at a working lunch with the prime minister of Singapore, Lee Hsien Loong.
The previous US stance, said Bruce Klingner of the Heritage Foundation, was that "we don't deploy a president to negotiate a treaty, we deploy a president to sign a treaty where we know where every piece of punctuation is on that piece of paper".
"One of my worries is that we come out of this Singapore summit with something that looks remarkably like the Six Party Talks or anything that the president has previously criticised but it is hyped as something that's historic and new and groundbreaking," he added.
The North's official KCNA news agency called the summit "historic", saying it would take place in a "changed era" and "under the great attention and expectation of the whole world".
Kim would exchange "wide-ranging and profound views" on issues including "building a permanent and durable peace-keeping mechanism on the Korean peninsula" and "realising the denuclearisation of the Korean peninsula", it added.
It formally referred to Trump by his full name in the Monday report, including his middle initial -- the first time it has done so.
Kim's sister and close aide Kim Yo Jong is also in Singapore, and is believed to have travelled separately on the ageing Soviet-made Ilyushin-62 that is the leader's personal aircraft.