North Korea agreeing to discuss denuclearisation “is evidence that President [Donald] Trump’s strategy to isolate the Kim regime is working,” US Vice-President Mike Pence has said.
He said the US had made “zero concessions” and “consistently increased the pressure” on North Korean leader Kim Jong-un.
An unprecedented summit between the two leaders is due to take place by May.
It comes only months after the pair hurled insults at each other.
Mr Trump has hailed the dizzying shift in North Korea’s position as “great progress” but said sanctions would remain in place.
South Korean envoys earlier briefed the US president on the meeting they had this week with Mr Kim, saying he was now “committed to denuclearisation”.
South Korea’s President Moon Jae-in said the news of the Kim-Trump meeting had come “like a miracle”.
“If President Trump and Chairman Kim meet following an inter-Korean summit, complete denuclearisation of the Korean peninsula will be put on the right track in earnest,” he said.
However, correspondents say the North has halted missile and nuclear tests during previous talks, only to resume them when it lost patience or felt it was not getting what it demanded.
Mr Trump’s strategy has been roundly praised by the South Koreans.
Chinese President Xi Jinping also telephoned him on Friday to welcome the development and urge all sides to show goodwill and avoid doing anything that could impede the improving situation on the Korean peninsula.
The US Secretary of State Rex Tillerson, speaking in Djibouti on an African trip, said of Kim Jong-un: “What changed was his posture in a fairly dramatic way.
“In all honesty, that came as a little bit of a surprise to us, as well that he was so forward-leaning in his conversations with the delegation from South Korea.”
In recent months, Mr Trump has belittled Mr Kim as the “rocket man”, threatening him with “fire and fury“, while Mr Kim has called Mr Trump “a mentally deranged US dotard”.
The speed of events appears to have caught Mr Tillerson off-guard – on Thursday he said the US was “a long way” from direct talks.
There has been no mention of the developments as yet on North Korean state media.