Pyongyang is also willing to close its main nuclear complex in Nyongbyon if the United States takes reciprocal action, Moon said.
"I don't think President Moon got everything he was seeking, but Kim gave Moon some tangible things for which he can take credit and some forward progress in terms of beginning a more substantive discussion and increased activity focused on denuclearization", said Michael Madden, an analyst at the Stimson Centre's 38 North in Washington.
Kim said he and Moon agreed to remove all nuclear weapons and threats from the Korean Peninsula.
After a day of ceremonials and lunch, the two leaders held a two-hour summit meeting, with talks scheduled to continue tomorrow.
On Wednesday evening, Moon's party will dine at a new fish restaurant in Pyongyang opposite Mansu hill, where giant statues of Kim's predecessors - his grandfather Kim Il Sung and father Kim Jong Il - look out over the city.
Kim sent a letter to the White House asking to meet with President Donald Trump for a second summit to follow up on their first highly publicized meeting in Singapore in June. They continued most every year until 2014, then were revived during North Korea's celebrations of the 70th anniversary of its state founding earlier this month.
Hanham said North Korea had made similar offers during previous rounds of negotiations, but the steps it had ultimately taken - demolishing a cooling tower at Yongbyon in 2008 for example - had been easily reversed.
"These moves are expected to help resolve the worldwide community's doubts toward North Korea's pre-emptive dismantling moves in the past as a mere show", he said, according to a pool report. Moon also appeared to be making good on his proposals to help build up the North's infrastructure and open cross-border rail links.
Possibly signaling a breakthrough, Trump welcomed the outcome of the inter-Korean summit in a Twitter message.
South Korean President Moon Jae-in, right, and North Korean leader Kim Jong Un walk together at the Paekhwawon State Guesthouse in Pyongyang, North Korea, Wednesday, Sept. 19, 2018.
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Though North Korea has unilaterally stopped nuclear and missile tests, it did not allow worldwide inspections of the dismantling its only known nuclear test site in May, drawing criticism that its action was for show and could be easily reversed.
It also said the two leaders have also agreed on a Pyongyang art troupe visiting Seoul for performances in October.
The two Koreas agreed to begin construction to reconnect railways and roads linking the countries within this year.
To further promote reconciliation, the divided Koreas have agreed to soon establish a new joint facility for more frequent and freer reunions of families separated since the end of the Korean War.
It would also force an extraordinary level of cooperation between two Cold War foes that have no formal avenues for regular contact and are still technically at war.
Prior to it, the leaders signed a comprehensive agreement on military tension reduction as a result of their third bilateral summit.
Such steps include setting up a 10-kilometer buffer zone along their border where all artillery drills or regiment-level field maneuvers will be prohibited, according to the military agreement.
The two Koreas will continue to jointly take part in worldwide sporting events, including the upcoming 2020 Olympic Games, the leaders said in their Pyongyang declaration.
The first hint of a possible joint bid came last week when South Korea's Yonhap news agency quoted the country's sports minister Do Jong-hwan as saying Seoul planned to propose the idea during this week's Pyongyang meeting.