U.S. President Donald Trump meeting with North Korean leader Kim Jong-un is shown on television screens at an electronics retail store on June 12, 2018 in Seoul, South Korea.

U.S. President Donald Trump said on Friday that U.S. diplomats had a "very productive meeting" with North Korean officials, and he announced his summit later this month with North Korean leader Kim Jong Un would be held in Vietnam's capital, Hanoi.

"My representatives have just left North Korea after a very productive meeting and an agreed upon time and date for the second Summit with Kim Jong Un. It will take place in Hanoi, Vietnam, on February 27 & 28," Trump said on Twitter.

"I look forward to seeing Chairman Kim & advancing the cause of peace!" he said.

Earlier this week, Trump announced the dates for the second summit with Kim and said it would be held in Vietnam, but the city had not been disclosed.

Stephen Biegun, the U.S. special representative for North Korea, held three days of talks in Pyongyang to prepare for the summit, the State Department said on Friday.

It said Biegun had agreed with his counterpart Kim Hyok Chol to meet again ahead of the summit.

In their talks in Pyongyang, from Wednesday to Friday, Biegun and Kim Hyok Chol "discussed advancing President Trump and Chairman Kim's Singapore summit commitments of complete denuclearization, transforming U.S.-DPRK relations, and building a lasting peace on the Korean Peninsula," the State Department said.

Its statement, which referred to North Korea by the acronym for its official name, the Democratic People's Republic of Korea, gave no indication of any progress in the talks.

Just weeks ahead of the planned summit to follow on from an unprecedented first meeting between the leaders in Singapore last June, the two sides have appeared far from narrowing differences over U.S. demands for North Korea to give up a nuclear weapons program that threatens the United States.

Biegun said last week his Pyongyang talks would be aimed at seeking progress on commitments made in Singapore and mapping out "a set of concrete deliverables" for the second summit.

He said Washington was willing to discuss "many actions" to improve ties and entice Pyongyang to give up its nuclear weapons and that Trump was ready to end the 1950-53 Korean War, which concluded with an armistice, not a peace treaty.