A US negotiator has called on North Korea to provide a detailed account of its weapons to seal a peace deal.
In his first remarks in months, US Special Envoy Stephen Biegun said that President Donald Trump was ready to offer a future that includes diplomatic relations and economic aid.
Mr Trump is expected to hold a second summit with the North Korean leader, Kim Jong-un, in around one month and has said that he would announce the exact date and venue early next week.
The president told reporters at the White House: "I think most of you know where the location is. I don't think it's a great secret."
Vietnam has offered to host the talks.
Mr Trump added: "We've made tremendous progress with North Korea."
His and Mr Kim’s summit in Singapore last June was the first ever between leaders of the two countries that never formally ended the Korean War.
The meeting produced a document in which Mr Kim pledged to work towards the "denuclearisation of the Korean peninsula".
Mr Biegun said that the US administration was "clear-eyed" and prepared for contingencies if talks fail.
This week, the Director of National Intelligence, Dan Coats, told the Senate Intelligence Committee that "North Korea is unlikely to give up all of its nuclear weapons and production capabilities".
In contrast, President Trump has stated that there is "a decent chance" of North Korea giving up its nuclear weapons.
Mr Biegun painted an upbeat picture at ending decades of hostility despite repeated failures in the past, saying that Mr Trump "is unconstrained by the assumptions of his predecessors".
Speaking at Stanford University in California, he said: "I have this perfect outcome moment where the last nuclear weapon leaves North Korea, the sanctions are lifted, the flag goes up in the embassy and the treaty is signed in the same hour.
"Now that's an ideal, I know, and these things are going to move haltingly along different courses. But they can also be mutually reinforcing."
Preparing the summit, the State Department said Mr Biegun would travel on Sunday to South Korea and also meet his North Korean counterpart.
Mr Biegun said the United States would ask North Korea for negotiations on verifying that it is giving up its nuclear weapons.
"Before the process of denuclearisation can be final, we must have a complete understanding of the full extent of the North Korean WMD and missile programmes through a comprehensive declaration."
"We must reach agreement on expert access and monitoring mechanisms of key sites to international standards, and ultimately ensure the removal or destruction of stockpiles of fissile material, weapons, missiles, launchers and other weapons of mass destruction."
Rejecting criticism that the Singapore declaration was vague, he said that Mr Kim has committed - both at the summit and in follow-up talks with the American Secretary of State, Mike Pompeo - to "the dismantlement and destruction" of all plutonium and uranium sites, not only its signature Yongbyon facility".
North Korea watchers believe the regime is foremost interested in easing international sanctions, which were tightened in 2017 after the regime's missile and nuclear tests raised fears of a new war.
Mr Biegun said President Trump was prepared to assist Mr Kim in building "a brighter economic future" and gave nuance to the repeated US insistence that it will not ease sanctions until denuclearisation.
"We say we will not lift sanctions until denuclearisation is complete. That is correct. We didn't say we won't do anything until you do everything," he said.
