Earlier, both Trump and Kim had expressed hope for progress on improving relations and on the key issue of denuclearisation, in their talks in the Vietnamese capital, Hanoi.

"The two leaders discussed various ways to advance denuclearization and economic driven concepts," White House spokeswoman Sarah Sanders said. "No agreement was reached at this time, but their respective teams look forward to meeting in the future.”

Trump had been scheduled to hold a "joint agreement signing ceremony" with Kim at the conclusion of their summit talks, according to an earlier White House announcement.

Both leaders left the venue of their talks, the French-colonial-era Metropole hotel, at 1.25 p.m. (0625), without attending a planned lunch together, and returned to their hotels.

Read: Donald Trump, Kim Jong Un Optimistic in 2nd Nuclear Summit

Trump is now due to hold a news conference at 2 p.m. (700 GMT)

News of the change in schedule sent South Korea's currency lower and knocked regional stock markets.

Earlier Kim and Trump, seated across from each other at a conference table, appeared confident of progress.

“If I’m not willing to do that, I won’t be here right now,” Kim told reporters through an interpreter, when asked if he was ready to give up his nuclear weapons.

Trump, responding to that, said: "That might be the best answer you’ve ever heard.”

Kim did not elaborate on what "denuclearisation" would entail, but asked if he was ready to take concrete steps, Kim said they had just been talking about that.

While the United States is demanding North Korea give up all of its nuclear and missile programmes, the North wants to see the removal of a U.S. nuclear umbrella for its Asian allies such as South Korea and Japan.

The two leaders' summit in Singapore in June, the first between a sitting U.S. president and a North Korean leader, produced a vague statement in which Kim pledged to work toward denuclearisation of the Korean peninsula.

But there has been little progress since.

REUTERS