Trump said two days of talks in the Vietnamese capital Hanoi had made good progress in building relations and on the key issue of denuclearisation, but it was important not to rush into a bad deal.

"It was all about the sanctions," Trump said at a news conference after the talks were cut short. "Basically, they wanted the sanctions lifted in their entirety, and we couldn't do that."

The United Nations and the United States ratcheted up sanctions on North Korea when the reclusive state undertook a series of nuclear and ballistic missile tests in 2017, cutting off its main sources hard cash.

Trump and Kim cut short their talks, skipping a planned working lunch at the French-colonial-era Metropole hotel after a morning of meetings.

Read: Trump, Kim Jong Un End Vietnam Summit with No Agreement

"Sometimes you have to walk, and this was just one of those times," Trump said, adding "it was a friendly walk".

He later left Vietnam to return to Washington.

Failure to reach an agreement marks a setback for Trump, a self-data-styled dealmaker under pressure at home over his ties to Russia and testimony from Michael Cohen, his former personal lawyer who accused him of breaking the law while in office.

Trump said Cohen "lied a lot" during Congressional testimony in Washington on Wednesday, though he had told the truth when he said there had been "no collusion" with Russia.

The collapse of the talks raised questions about the Trump administration's preparations and about what some critics see as his cavalier data-style of personal diplomacy.

Since their first summit in Singapore in June, Trump has stressed his good chemistry with Kim, but there have been doubts about whether the bonhomie could move them beyond summit pageantry to substantive progress on eliminating a North Korean nuclear arsenal that threatens the United States.

Things had appeared more promising when the leaders met on Wednesday, predicting successful talks before a social dinner with top aides.

The White House had been confident enough to schedule a "joint agreement signing ceremony" at the conclusion of talks. Like the lunch, the ceremony did not take the place.

REUTERS