Joseph Yun, speaks to media in Bangkok, Thailand. Dec. 15, 2017. AP-Yonhap

North Korean leader Kim Jong-un won't negotiate denuclearization with the United States, as he has more powerful weapons and support from Russia, Joseph Yun, a former U.S. envoy on North Korea policy, said Friday, dismissing any chances for dialogue as a "non-starter."

Yun, who served as special representative for North Korea policy during the early phase of the first Donald Trump administration, made the remarks at a symposium co-hosted by Triforum and the Asiatic Research Institute, Korea University, discussing the global order in light of Trump's election to his second term.

Trump's return to the presidency has sparked speculation about his resuming personal diplomacy with Kim following their two landmark summits in Singapore and Vietnam.

Since the Hanoi summit ended without a deal in 2019, no dialogue has taken place between Washington and Pyongyang, including during the following Joe Biden administration.

"In the absence of any deal, North Korea has become more threatening. Their weapons have become more powerful," Yun said, noting that now North Korea is no longer an isolated pariah, thanks to "the strongest possible support from Russia."

"We have to accept reality. There is no chance that North Korea will start any negotiation with anyone which (requires) upfront complete denuclearization. That's a non-starter," he noted.

Instead, the U.S. might need to start with "small steps," such as weapons reduction, freezing new technology and fostering some kind of engagement between South and North Korea, while building on agreements Trump already made with Kim in order to eventually seek denuclearization, he said.

"If I were, you want to make sure that Singapore agreement is still valid on both sides. ... Where the Trump administration left off, which is in Hanoi. Hanoi (dialogue), I think, if you just added pieces to it, could be made into a deal," Yun noted.

"We cannot jump to complete denuclearization. CVID (complete, verifiable and irreversible denuclearization) as we used to call it, I'm sorry, but it's kind of dead."

Joseph Yun, right, answers questions from reporters following a meeting with Japanese and South Korean chief nuclear negotiators at the Iikura Guesthouse in Tokyo, April. 25, 2017. Yonhap

Drawing on North Korea's dispatch of troops to fight for Russia against Ukraine, Yun said the decision was a "very smart" move in securing money and weapons technology from Russia, effectively rendering international sanctions "out of the window."

At the forum, Robert O'Brien, former national security adviser to Trump during his first term, echoed Yun's assessment, saying that reaching a deal with North Korea "is not going to be easy."

"The best we can do is trying to assure our South Korean friends ... that the U.S. nuclear umbrella covers South Korea," he said.

O'Brien predicted that Trump's tariff plans in his second term wouldn't negatively affect South Korea, citing South Korean companies' investments and factories operating in the U.S.

During the campaign, Trump said, if reelected, he will impose a minimum 10 percent tariff on imported products and as high as 60 percent import tariffs on Chinese goods.

"I think South Korea is going to do very well," he said, adding Trump has "made it very clear that the countries that invest in America and that produce products from their factories in America are not going to be subject to the tariffs that he's talking about." (Yonhap)