North Korea has pledged to destroy all its nuclear material enrichment facilities, according to the US special envoy for the country, Stephen Biegun, reports BBC.
He said the promise had been made to US Secretary of State Mike Pompeo when he visited North Korea in October.
However Pyongyang has not confirmed making any such pledge.
Mr Biegun also said that North Korea must provide a complete list of its nuclear assets before any deal can be reached.
Experts believe the North has more than one undeclared nuclear fuel enrichment site aside from the known facility at Yongbyon, north of Pyongyang, and question how the destruction of all facilities could be fully verified.
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.
Stephen Biegun has been Washington's top envoy to North Korea for five months but he gave a detailed public accounting of his approach for the first time in a speech at Stanford University in California.
Mr Biegun said President Trump was "ready to end this war".
"We're not going to invade North Korea. We are not seeking to topple the regime," he said.
Mr Biegun - who will travel to South Korea on Sunday before meeting North Korean officials - also said Washington was willing to discuss a range of trust-building measures with Pyongyang.
He said Kim Jong-un had committed, in his talks with Mr Pompeo, to "the dismantlement and destruction" of all its plutonium and uranium facilities, which provide the material for nuclear weapons.
But he reiterated that the US would not lift sanctions until denuclearisation was complete, demanding "a complete understanding of the full extent of the North Korean WMD [weapons of mass destruction] and missile programmemes through a comprehensive declaration".
North Korea has long refused to give a full account of its nuclear capacity, and the means by which any surrendering or dismantling of nuclear arms will be verified has always been a sticking point in negotiations.
The country has one known nuclear fuel production facility at Yongbyon, which has been the source of plutonium for its nuclear weapons programmeme. Uranium is also enriched there, according to experts.
