US President Donald Trump has said there was a "substantial chance" his summit with North Korean leader Kim Jong Un will not take place as planned on 12 June.

It comes amid concerns that Mr Kim is not committed to denuclearisation.

Mr Trump raised doubts about the Singapore summit in talks with South Korean President Moon Jae-in, who travelled to the US to urge Mr Trump not to let a rare opportunity with reclusive North Korea get away.

If the summit is called off or fails, it would be a major blow to what Trump supporters hope will be the bigges tdiplomatic achievement of his presidency, and a huge disappointment for Mr Trump.

"There's a very substantial chance ... it wo’nt work out. And thats OK," Mr Trump told reporters. "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."

Mr 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

Mr 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 United States and North Korea.

It was unclear whether Mr 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 after decades of tension on the Korean peninsula and antagonism with the US over its nuclear weapons programme.

"Trump doesn’t want to look like he wants this summit more than Kim does," said Bonnie Glaser, an analyst at the Center for Strategic and International Studies in Washington.

"It’s a smart move to say that he is willing to postpone. But to be credible, the president really has to be willing to walk away and I’m not sure he is. "

Aides said Mr Trump has privately been wondering whether Mr Kim is serious about the summit after an abrupt change in tone last week from North Korea, which suggested the meeting could be cancelled if it was pushed toward "unilateral nuclear abandonment."

Mr 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 United States and North Korea.

It was unclear whether Mr 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 after decades of tension on the Korean peninsula and antagonism with the US over its nuclear weapons programme.

"Trump doesn’t want to look like he wants this summit more than Kim does," said Bonnie Glaser, an analyst at the Center for Strategic and International Studies in Washington.

"It’s a smart move to say that he is willing to postpone. But to be credible, the president really has to be willing to walk away and I’m not sure he is. "

Aides said Mr Trump has privately been wondering whether Mr Kim is serious about the summit after an abrupt change in tone last week from North Korea, which suggested the meeting could be cancelled if it was pushed toward "unilateral nuclear abandonment."