US President Donald Trump will hold a second summit with North Korean leader Kim Jong Un in late February but will maintain economic sanctions on Pyongyang, the White House said on Friday after Trump met Pyongyang's top nuclear negotiator.

The announcement came amid a diplomatic flurry in Washington surrounding the visit of Kim Yong Chol, a hardline former spy chief, and marked a sign of movement in a denuclearisation effort that has stalled since a landmark meeting between Trump and the North Korean leader in Singapore on June 12.

"President Donald J Trump met with Kim Yong Chol for an hour and a half to discuss denuclearisation and a second summit, which will take place near the end of February," White House spokeswoman Sarah Sanders said. She said a location would be announced later.

The summit was announced even though there has been no indication of any narrowing of differences over US

demands that North Korea abandon a nuclear weapons program that threatens the United States and Pyongyang's demands for a lifting of punishing sanctions.

Sanders said that Trump's talks with the North Korean envoy were productive but added that the United States "is going to continue to keep pressure and sanctions on North Korea."

South Korea's presidential office said it expected the upcoming summit to be a "turning point to lay the firm foundation for lasting peace on the Korean peninsula."

South Korea will work with the United States and other countries to "achieve concrete and practical results towards complete denuclearisation and a lasting peace regime through the North Korea-U.S. summit...," presidential spokesman Kim Eui-kyeom said in a statement yesterday.

South Korea will also expand inter-Korean dialogue to help a successful meeting between Trump and Kim, he added.

The first summit produced a vague commitment by Kim Jong Un to work towards the denuclearisation of the Korean peninsula, but he has yet to take what Washington sees as concrete steps in that direction.

Nevertheless, both he and Trump had expressed an interest in arranging a second meeting, something some US-based analysts see as premature.

Critics of US efforts say the first summit only boosted Kim's international stature without much to show for it, and some believe Trump may see a second meeting as a way of distracting from his domestic troubles.

Trump declared just after the Singapore meeting that the nuclear threat posed by North Korea was over. But hours before Kim Yong Chol's arrival on Thursday, the US president unveiled a revamped US missile defense strategy that singled out the country as an ongoing and "extraordinary threat."

Harry Kazianis, an analyst at the conservative Washington-based Center for the National Interest, called the agreement to hold another summit positive. But he added: "Both nations must now show at least some tangible benefits from their diplomatic efforts during a second summit, or risk their efforts being panned as nothing more than reality TV."

Communist-ruled Vietnam, which has good relations with both the United States and North Korea, has been widely touted as the most likely site of the next summit. There has also been speculation about other possible venues, including Bangkok, Hawaii, or a return to Singapore.

A senior US administration official said there was an exchange of letters for the leaders during the White House meeting, but gave no details of their content.

On his last visit to Washington in June, Kim Yong Chol delivered a letter from Kim Jong Un to Trump that helped overcome obstacles ahead of the summit in Singapore.

Kim Yong Chol, regarded as a member of Kim Jong Un's inner circle, also had talks with Secretary of State Mike Pompeo and US special representative on North Korea, Stephen Biegun.

US-based analysts said that North Korea, which has developed missiles and nuclear weapons in defiance of U.N. Security Council resolutions, would likely be seeking a clearer message from the Trump administration on any concessions it may be willing to make.

South Korean Foreign Minister Kang Kyung-wha said on Wednesday that if North Korea took concrete steps toward abandoning its weapons programs, Washington could offer a formal end to the 1950-53 Korean War, humanitarian aid or a permanent channel for bilateral dialogue.