WASHINGTON (Reuters) - The U.S. special representative for North Korea is traveling to Hanoi on Tuesday to continue preparations for a second summit between U.S. President Donald Trump and North Korean leader Kim Jong Un to be held next week in Vietnam, the State Department said.

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State Department spokesman Robert Palladino told a news briefing he had no details of the meetings Stephen Biegun would have in Hanoi.

Biegun spent three days in North Korea from Feb. 6-8, a trip he said was aimed at agreeing on “concrete deliverables” for the Feb. 27-28 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 United States has been demanding that North Korea give up a nuclear weapons program that threatens the United States, and Trump has been eager for a second summit even though a first meeting in Singapore in June meeting produced only vague commitments from Kim and little concrete progress since.

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.

Asked whether the United States would consider lifting sanctions, Palladino said: “We’ve been clear on sanctions. These are the world’s sanctions and that is something that ... will continue to be maintained until we’ve achieved our final result of a fully, finally, verified denuclearization.”

However, he then added: “But I don’t want to get ahead on ... any further details on what’s being negotiated regarding that question.”

Palladino did not respond directly when asked about reports that the two sides were discussing the exchange of liaison officers and declaring an end to the 1950-53 Korean War.

“I am not going to get ahead of diplomatic conversations, or ahead of the president. A lot of things are being discussed and we are very much looking forward to next week,” he said.

U.S. Secretary of State Mike Pompeo said of Kim last week it was “time for him to deliver,” but the Trump administration has moved away from demands that North Korea give up its nuclear weapons immediately and has appeared to adopt a more gradual, reciprocal approach Pyongyang has insisted on.

On Tuesday, Trump reiterated that he wants North Korea to end its nuclear program, but he is in no rush and has no pressing time schedule for Pyongyang to ultimately denuclearize.

Pompeo said the United States aimed to “get as far down the road as we can” with North Korea in the next two weeks and that Biegun’s team would discuss all issues covered in Singapore.

Asked on Thursday how important a formal end of the Korean War was in the discussions, Pompeo said: “It’s something we’ve had a lot of talks about.”

He said Trump and Kim would also be looking at the “denuclearization pillar they agreed to” in Singapore and how to reduce tension and military risk “so we can get peace and security on the peninsula as well.”

(Corrects spelling of Pompeo in paragraph 11.)