"Basically, they wanted the sanctions lifted in their entirety," said Trump. "And we couldn't do that.
"Sometimes you have to walk and this was just one of those times," Trump added. "I'd much rather do it right than do it fast."
In the prelude to the second meeting between the US president and the North Korean leader, the White House programme said there would be a joint agreement signing ceremony.
However the two leaders departed without signing any deals.
Better future together?
During the meeting in Vietnam, Trump suggested a better economic future for a nuclear-free North Korea, at one point saying there was "AWESOME" potential.
In their first summit in Singapore in June 2018, the two signed a document in which Kim pledged to work toward complete denuclearisation of the Korean peninsula.
Progress faltered with the two sides disagreeing on the implementation of the pledge.
As in Singapore, the two leaders played up the pomp and circumstance. They appeared to share jokes in front of reporters and they went for a poolside stroll around the gardens of the Metropole Hotel. It echoed a promenade in Singapore, where the two men bonded over Trump's car - the "Beast".