Kim Jong-un said he still has "confidence" in blocked peace talks with Donald Trump when North and South Korea announced a historic new summit between the two nations in less than two weeks.
Moon Jae-in will be the first South Korean president to visit Pyongyang in more than 10 years as he travels to the North Korean capital on September 18 and 20 to speak with Kim. It will be the couple's third meeting since April.
The summit between the two Koreas will be an important indicator of whether nuclear negotiations with the US will continue, and the South Korean Prime Minister has played a major role in keeping these talks alive.
South Korea said it had forwarded a message from Mr. Trump to Mr. Kim, who in turn sent a message to Seoul to take to the US.
In comments sent on Thursday by both the North Korean media and the South Korean mediators, Kim reaffirmed his commitment to a nuclear-free Korean peninsula and the suspension of all future long-range missile testing.
"Chairman Kim Jong Un has made it clear on several occasions that he is determined to reduce nuclear weapons, and he expressed frustration over the skepticism in the international community regarding his commitment," said Chung Eui-yong, Moon's national security adviser the head of the South Korean delegation in Pyongyang, told reporters in Seoul.
"He said he had taken the necessary steps to denuclearise as a preventive measure, and he wants these goodwill measures to be met with goodwill measures."
The North Korean leader told the Southern officials that his trust in Mr. Trump had remained "unchanged" since a historic summit in Singapore in June and that he wanted to democratize and build friendly relations with the US before the end of Trump's first term, Chung said ,
Chung added that during the summit later this month, Mr. Kim and Mr. Moon would discuss "practical measures" for denuclearization.
Mr. Moon is considered eager to keep the diplomacy alive so that he can advance his ambitious North engagement plans that the US needs to support to succeed.
The inter-Korean summit will take place on the eve of a meeting of United Nations leaders in New York in late September, but Seoul said on Thursday it was unlikely that Kim would attend.
Seoul has expressed interest in meeting Kim and Trump in New York, and Trump, who is in the growing turmoil in the country, has hinted that another summit could take place.
As the Seouls push ahead with the summits and inter-Korean engagement, they try to persuade Washington and Pyongyang to continue at the same time with peace and denuclearization processes in order to overcome a growing controversy over the succession of diplomacy.
Seoul and Pyongyang both want a statement to officially end the Korean War in 1950-53.
US officials have insisted that a peace declaration, which many see as a precursor to the North and ultimately demand the removal of all US troops from the Korean peninsula, can only occur when North Korea takes more concrete action to abandon its nuclear weapons.
Such steps may include the preparation of a report on the components of its nuclear program, the approval of external inspections and the abandonment of a certain number of nuclear weapons in the early stages of the negotiations.
The Korean War ended with a truce, leaving the peninsula technically still at war.
Mr. Moon has made a statement at the end of the war an important premise on his peace agenda with North Korea.
Additional reporting from AP