The key to setting the stage for the historic summit between the Democratic People's Republic of Korea top leader Kim Jong-un and the United States President Donald Trump is whether the visiting DPRK high-ranking official and his US counterpart can settle the disagreements in denuclearization, experts said.

US Secretary of State Mike Pompeo and vice-chairman of the DPRK's Workers' Party of Korea Central Committee Kim Yong-chol entered their second day of meetings in New York on Thursday, after the two finished a 90-minute private dinner at a New York apartment on Wednesday night without providing details about their conversation.

On Thursday, Moscow said Kim Jong-un met the visiting Russian Foreign Minister Sergei Lavrov, in what is believed to be the first meeting between Kim and a Russian official.

The Russian Foreign Ministry said on Twitter in English, after releasing pictures of the two shaking hands, that "Lavrov was greeted by the Chairman of the State Affairs Commission of DPRK Kim Jong-un during his visit to Pyongyang".

Chinese Foreign Ministry spokeswoman Hua Chunying said on Thursday direct contact and dialogue between the leaders of Pyongyang and Washington is the key to resolving the nuclear issue on the Korean Peninsula. She added that the current situation on the peninsula breaks the deadlock that has lasted for several years, and it faces a historic opportunity for denuclearization.

"We encourage and support the leaders of both sides to show sincerity, interact positively and meet as scheduled and to jointly open the door to a denuclearized, peaceful, and prosperous future," said Hua, adding that with the realization of denuclearization, China is willing to continue to play an active and constructive role in establishing a long-term and effective peace mechanism on the peninsula.

However, there are "quite significant" differences between the US and the DPRK over denuclearization, the Republic of Korean's Yonhap News Agency reported on Wednesday.

Sue Mi Terry, senior fellow and Korea chair at the Center for Strategic and International Studies, said that the definition of denuclearizing, as understood by the US and the DPRK, is "very different, at least until now".

Terry said the US' concept of denuclearization always refers to the unilateral dismantlement of the DPRK's nuclear weapons program, which is "exactly what the DPRK is opposed to".

The DPRK's first vice-minister of foreign affairs Kim Kye-gwan said two weeks ago that "if the US is trying to drive us into a corner to force our unilateral nuclear abandonment, we will no longer be interested in such dialogue".

Ruan Zongze, executive vice-president of the China Institute of International Studies, said there are still many obstacles and differences that need to be overcome before the Kim-Trump dialogue.

"It is still not sure whether Pompeo and Kim Yong-chol and all the ongoing diplomacy are able to narrow that gap, but it is sure that a rapid denuclearization and the so-called 'Libya model' of denuclearization for the DPRK, which was expressed earlier by Trump's National Security Advisor John Bolton, was unrealistic for Pyongyang," he said.

The ROK Unification Minister Cho Myoung-gyon said on Wednesday that it will not be easy to narrow the gap and find common ground.

"But I think it would not be impossible," Cho said, adding Pyongyang's commitment to denuclearization was clear, citing the end of nuclear and missile tests, the demolition of a nuclear test site, and the two recent summits between ROK President Moon Jae-in and Kim Jong-un.

Zhou Jin and Ren Qi contributed to this story.