US President Donald Trump says there is a "substantial chance" his summit with North Korean leader Kim Jong Un will not take place as planned on June 12 amid concerns that Kim is resistant to giving up his nuclear weapons.
Trump raised doubts about the Singapore summit in talks with South Korean President Moon Jae-in, who came to Washington to urge Trump not to let a rare opportunity with reclusive North Korea slip away.
If the summit is called off or fails, it would be a major blow to what Trump supporters hope will be the biggest diplomatic achievement of his presidency, and a huge disappointment for the president himself.
"There's a very substantial chance ... it won't work out. And that's OK," Trump told reporters on Tuesday. "That doesn't mean it won't work out over a period of time. But it may not work out for June 12. But there is a good chance that we'll have the meeting."
Trump said whether the meeting will be held as scheduled will be determined "pretty soon".
"North Korea has a chance to be a great country and I think they should seize the opportunity," he said.
Trump's Oval Office remarks were the strongest sign from him yet about the possibility of a delay or cancellation of what would be the first-ever summit between the leaders of the US and North Korea.
It was unclear whether Trump was truly backing away from a summit that he is eager to hold or whether he was strategically coaxing North Korea to the table.
The original purpose of Trump and Moon's meeting was to fine-tune a joint strategy for dealing with Kim. Instead it has become more of a crisis session after Pyongyang last week threatened to pull out of the planned summit.
The White House was caught off-guard when, in a dramatic change of tone, North Korea condemned the latest US-South Korean air combat drills, suspended North-South talks and threw into doubt the summit with Trump if Pyongyang was pushed toward "unilateral nuclear abandonment".
Aides said Trump has privately been wondering whether Kim is serious about the summit after the abrupt change in tone.
Trump heaped praise on Moon as an "extremely competent" leader despite some concerns voiced by US officials that Moon might be too willing to compromise with Kim.
Moon was optimistic about the summit in his Oval Office remarks. He said he realised many were sceptical in the US about the summit "but I don't think there will be positive developments in history if we just assume that, because it all failed in the past, it will fail again".
Trump on Tuesday reiterated that there are certain conditions that must be met and if North Korea refuses, the meeting will not take place. He said he would like a deal to commit North Korea to denuclearise over a "short period of time".