Pyongyang would be willing to allow American experts to develop North Korean remnants if the United States removes partial sanctions, Ri said.
"If the United States removes the partial sanctions, the economy, and the livelihoods, we will permanently and completely disassemble all material from nuclear material production facilities in Yongbyon, including plutonium and uranium," he said. .
Ri only commented a few hours after Trump left talks with North Korean leader Kim Jong Un in Vietnam. The American President said he did so because North Korea had demanded that all sanctions against Pyongyang be lifted.
"Basically, they wanted the sanctions to be completely abolished and we couldn't do that," said Trump at the press conference following the summit.
Ri seemed to suggest that Trump's claims were wrong, saying North Korea was only asking for five of the 11 sanctions imposed by the United Nations Security Council to try to kill Pyongyang for repetitive nuclear and ballistic missile tests.
These sanctions are being pursued by Kim for the improvement of the North Korean economy and for the livelihood of its people, one of the young North Korean leaders' goals for the country.
However, analysts say Pyongyang still holds the key to nuclear weapons survival.
According to the translator, the North Korean proposal can be considered as "the greatest downsizing measure in the current phase relative to the current confidence level".
Ri also said that North Korea is committed to permanently stopping testing of nuclear weapons and long-range missiles.
But the United States also demanded "one more thing at the top of Yongbyon (the demolition)," the only publicly known facility in the country to produce fissile material for nuclear weapons.
After that, Ri said, "It was clear that the United States was not ready to accept our proposal."
Trump characterized the lack of business only as a short-term disappointment, though he hoped that he could enter the negotiations to show a new, concrete path to nuclear decomposition. The significant agreement reached in Hanoi may have frustrated the embarrassing headlines of former Trump lawyer Michael Cohen, who confirms that the president is a racist.
The personal chemistry that Trump cultivated — and loudly trumpeted — was left untouched by the young despotist, the president insisted.
And the summit ended peacefully without any people storming it.
Yet, American and North Korean officials continue to contradict the exact definition of denucleation, which is the stated purpose of their efforts.
"We have a certain vision, and this is not exactly our vision, but it is much closer than a year ago, and I think we will finally be there," said Trump at his summit.
Trump also told Kim that he had put particular emphasis on eliminating sanctions for his economy and for the first time helping the negotiating table.
CNN Yoonjung Seo contributed to this report.