The two are due to meet on Tuesday on the resort island of Sentosa for their high-stakes summit, the first-ever talks between a US and North Korean leader and the culmination of a head-spinning diplomatic dance.

Such a meeting was unthinkable just months ago when Trump and Kim were exchanging insults and threats that raised fears of war in the region. But a series of diplomatic overtures involving North Korea, South Korea and the United States reduced tensions and led Trump in March to quickly accept Kim’s invitation to meet.

Trump initially touted the potential for a grand bargain with North Korea to rid itself of a nuclear missile programme that has advanced rapidly to threaten the United States, insisting he would swiftly achieve what previous US administrations have failed to do.

But he has since lowered expectations, saying the talks would be more about starting a relationship with Kim for a negotiating process that would take more than one summit. This has included backing away from an original demand for North Korea's swift denuclearisation.

Kim has given little sign of any willingness to dismantle his nuclear programme, which experts believe he sees as vital to the survival of his family's dynastic rule.

However, Trump and his aides insist that a US-led "maximum pressure" campaign of the toughest-ever economic sanctions, diplomatic action and military threats is what has drawn Kim to the negotiating table.

Trump frequently has boasted of his negotiating prowess as a former real estate developer, and his ability to read people, even though his businesses have declared multiple bankruptcies.

He said on Thursday that he didn't think he had to prepare very much for the summit and that "it's about attitude". But some US officials have questioned whether Trump was doing enough to get up to speed.

Trump told reporters in Canada on Saturday any agreement with Kim would be "spur of the moment," underscoring the uncertain outcome of what he called a "mission of peace".

That came as Trump threw the Group of Seven's efforts to show a united front into disarray after he became angry with Canadian Prime Minister Justin Trudeau, and said he might double down on import tariffs by hitting the sensitive auto industry.

Trump's bombshell announcement that he was backing out of the G7 communique, made after he left the summit in Canada early, torpedoed what appeared to be a fragile consensus on the trade dispute between Washington and its top allies.

Reuters