American diplomacy with North Korea "is still very much alive", and US President Donald Trump remains open to another meeting with North Korean leader Kim Jong Un despite the abrupt end to last month's summit in Hanoi, said the US special envoy for North Korea, Mr Stephen Biegun.
The United States will continue to engage North Korea diplomatically to see if there are opportunities to reach agreements on confidence-building measures like opening liaison offices, he added.
But North Korea has not yet committed to full denuclearisation, and the US will not accept partial denuclearisation, Mr Biegun said on Monday in his first public comments since the Hanoi summit.
"This will be something we would like to get done in the President's first term. But ultimately, it requires the North Koreans to start, and the missing variable right now is that the North Koreans have to be similarly bought into that objective," he said at the Carnegie International Nuclear Policy Conference in Washington DC.
He stressed that the US remained wedded to its all-or-nothing approach to denuclearisation, as he ruled out an incremental, step-by-step approach that would see Pyongyang increasingly give up elements of its nuclear programmes in exchange for partial sanctions relief.
"We are not going to do denuclearisation incrementally. The President has been clear on that and that is a position around which US government has complete unity. Our goal, our objective, is the final fully verified denuclearisation of North Korea," said Mr Biegun.
But his comments were met with scepticism by the audience, who pressed him repeatedly on whether the administration's approach was realistic and what North Korea would get in return.
Conference moderator Helene Cooper of the New York Times asked: "If you don't do this incrementally, how can you get it all done? Why should North Korea believe that at the end of this rainbow they'll get a pot of gold?"
Mr Biegun replied that the US needed a "total solution", the philosophy behind Mr Trump's rejection of Mr Kim's proposal at the Hanoi summit to shut down Yongbyon nuclear facility in exchange for the lifting of United Nations sanctions imposed since 2016.
"We would have been lifting all the economic pressure that's been imposed upon North Korea for the totality of its weapons of mass destruction programmes... in exchange for only a portion of those weapons of mass destruction programmes. That would have put us in a very difficult position of essentially subsidising what would potentially be ongoing development of weapons of mass destruction in North Korea," he said.
Asked what the US was willing to offer North Korea if the lifting of sanctions was off the table until full denuclearisation was achieved, Mr Biegun said Mr Trump had laid out a vision of a bright economic future North Korea could enjoy if it denuclearised.
"The President bypassed this process question at the Hanoi Summit... by challenging Kim Jong Un to go big, to move fast. Let's go for a big proposal here to eliminate these weapons of mass destruction programmes," he said.
The US envoy added: "The President has created the space and momentum for diplomacy, the missing variable is North Korea itself has to also fully commit to the elimination of its weapons of mass destruction and affiliated programmes, and if they do that, we will get to this endpoint quickly."
Addressing reports last week of increased activity at North Korea's Sohae rocket-testing facility, Mr Biegun stressed that Pyongyang had not launched any missiles, and he urged the audience not to read too much into the commercial satellite photographs.
"What Kim Jong Un will decide to do may very much be his decision and his alone… We don't know that it's intended to send any particular statement to us," he said, adding that Mr Trump had made it clear that the US would be "very disappointed" if Pyongyang were to resume testing.