North Korea has pledged to destroy all its nuclear material enrichment facilities, according to the US special envoy for the country, Stephen Biegun.
He said the promise was made to US Secretary of State Mike Pompeo when he visited North Korea in October.
But Mr Biegun said North Korea must provide a complete list of its nuclear assets before any deal can be reached.
President Donald Trump had earlier claimed “tremendous progress” in talks between the countries.
Speaking in the Oval Office on Thursday, the president said he would soon announce the date and location of a planned second summit with North Korea’s Kim Jong-un.
The pair met in Singapore last year, the first meeting between a sitting US president and a North Korean leader, and signed an optimistic but vague declaration of their commitment to denuclearisation.
Since then little progress has been made.