A delegation of six U.S. officials led by special envoy Stephen Biegun landed at Noi Bai International Airport in Hanoi early on Thursday, a source told VnExpress.

Traveling with Biegun are officials specializing in economic development and North Korea in the U.S. National Security Council, the source said.

As planned, Biegun will meet with North Korean special envoy Kim Hyok-chol, who arrived in Hanoi on Wednesday night, to continue preparations for the second meeting between U.S. President Donald Trump and North Korean leader Kim Jong-un that has been scheduled for February 27-28 in the capital city of Vietnam.

U.S. State Department spokesman Robert Palladino told a news briefing on Wednesday he had no details of the meetings Stephen Biegun would have in Hanoi, Reuters reported.

Biegun spent three days in North Korea from February 6-8, a trip he said was aimed at agreeing on "concrete deliverables" for the coming Trump-Kim summit. The State Department said after those talks that Biegun agreed to hold further meetings with his counterpart Kim Hyok-chol ahead of the summit.

Biegun said after that trip his talks in North Korea had been "productive" but there was "hard work to do" before the summit.

The U.S. has been demanding that North Korea give up a nuclear weapons program that threatens the United States. The second summit will seek to build on the results achieved at the first summit in Singapore last June.

North Korea has been seeking a lifting of punishing U.S.-led sanctions, a formal end to the 1950-53 Korean War and security guarantees.