North Korea's foreign minister said early Friday that Pyongyang made a "realistic proposal" at leader Kim Jong Un's summit with U.S. President Donald Trump in Hanoi, Yonhap news agency reported.

In a highly unusual late-night statement at the North Korean delegation's hotel, Ri Yong Ho added Pyongyang was seeking partial sanctions relief, the South Korean agency reported, denying Trump's assertion it wanted them all lifted.

He said if the United States partially removed sanctions, North Korea could permanently dismantle all nuclear material production, including plutonium and uranium under U.S. observation.

Ri told reporters that Pyongyang was seeking partial sanctions relief, not a complete lifting of sanctions. Trump said he walked away from the summit because of unacceptable demands from Kim to lift U.S.-led sanctions.

Ri said if the two sides went through several levels of trust-building steps, Pyongyang would be willing to move forward with denuclearization.

In addition to offering to dismantle Yongbyon, North Korea offered to permanently halt nuclear tests, Ri told the news conference.

Trump said two days of talks in the Vietnamese capital had made good progress in building relations and on the main issue of denuclearization, but it was important not to rush into a bad deal.

Officials in Seoul on Thursday expressed regret for the failure to reach a deal on denuclearization of the Korean peninsula.

"(We) do feel regret that President (Donald) Trump and Chairman Kim Jong Un could not reach a complete agreement at today's summit," South Korea's presidential office spokesman Kim Eui Kyeom said in a statement to Yonhap news agency. "But it also appears that they have clearly made more meaningful progress than at any time in the past."

Seoul insisted Washington and Pyongyang have "made more progress than ever, even without an agreement."