Ri said the North was also ready to offer in writing a permanent halt of the country's nuclear and intercontinental ballistic missile tests and that Washington wasted an opportunity that "may not come again."
He said the North's position wouldn't change even if the United States offers to resume another round of dialogue.
Update 3 a.m. EST Feb. 28: Addressing reporters at a Thursday news conference, Trump said he has "not committed" to another summit with Kim.
“We’ll see if it happens,” Trump said, later adding: “I hope it will be soon, but it might not be for a long time.”
According to Trump and Secretary of State Mike Pompeo, Kim offered to dismantle North Korea’s Yongbyon nuclear complex, but not other facilities, if the U.S. lifted sanctions beforehand. Trump refused.
Trump also said Kim said he didn’t know that Otto Warmbier, an American college student who died after being held prisoner in North Korea, had been mistreated.
“He tells me he didn’t know about it, and I take him at his word,” Trump said.
Trump also said he doesn’t want to increase sanctions.
Update 2:30 a.m. EST Feb. 28: Trump is speaking to reporters after he and Kim were not able to reach a deal at their second summit in Vietnam.
“Sometimes you have to walk,” Trump said, adding that the countries disagreed about sanctions.
“They wanted sanctions lifted in their entirety, and we weren’t willing to do that,” Trump said.
Trump called the discussions “productive” and insisted that he and Kim still “have a good relationship.”
“He has a certain vision, and it’s not exactly our vision, but it’s a lot closer than it was a year ago,” Trump said. “I think, eventually, we will get there.”
Update 1:50 a.m. EST Feb. 28: Trump and Kim were unable to reach a denuclearization deal after a second day of talks in Vietnam came to a close earlier than anticipated, The Associated Press reported Thursday.
“No agreement was reached at this time, but their respective teams look forward to meeting in the future,” said White House Press Secretary Sarah Huckabee Sanders.
Trump and Kim originally had planned to sign a joint agreement at a ceremony Thursday, but that was canceled.
Read more here.
Update 10:55 a.m. EST Feb. 27: Trump said Wednesday in a tweet that he had a "great meeting and dinner with Kim Jong Un."
“Looking forward to continuing our discussions tomorrow!” he wrote.
The pair and their aides will meet Thursday for formal discussions.
Update 9:30 a.m. EST Feb. 27: Trump and Kim finished their meetings Wednesday afternoon after about two hours, The Associated Press reported. With aides in tow, the pair met for what the White House called a "social dinner." Trump left the Sofitel Legend Metropole Hanoi hotel before 9 p.m. local time, according to the AP.
Trump and Kim are scheduled to meet again Thursday before Trump makes the trip back to the U.S.
Update 7:32 a.m. EST Feb. 27: The White House said in a statement that it is limiting the number of U.S. reporters allowed at Trump's dinner meeting with Kim.
“Due to the sensitive nature of the meetings, we have limited the pool for the dinner to a smaller group,” the statement said.
>> See a photo from the dinner here
Update 7:12 a.m. EST Feb. 27: Trump and Kim shook hands as the met before dinner Wednesday at the Sofitel Legend Metropole Hanoi in Vietnam.
Appearing before reporters, Trump said: “It’s an honor to be with Chairman Kim. It’s an honor to be together in a country, Vietnam, where they have really rolled out the red carpet and they are very honored to have us.”
Trump told Kim that his country has “tremendous economic potential.”
Trump also said both leader “look forward” to the meeting.
“I thought the first summit was a great success, and I think this one, hopefully, will be equal or greater than the first.”
Original story: President Donald Trump and North Korean leader Kim Jong Un have kicked off their second summit in Hanoi, Vietnam.
According to The Associated Press, the pair, who previously met last June in Singapore, are meeting "for 20 minutes before sitting down for what the White House has described as a 'social dinner' together."
Secretary of State Mike Pompeo and Mick Mulvaney, the White House's acting chief of staff, also will be at Wednesday's dinner, the AP reported.
>> Read more trending news
The Associated Press contributed to this report.