Cho Myoung-gyon, the South's unification minister, said Seoul was abiding by international sanctions on Pyongyang despite President Moon Jae-in's calls for a step-by-step easing of pressure.

"One thing I would like to highlight here is that we are not going to open the Kaesong industrial complex soon," Cho said on a visit to Washington.

"The South Korean government has a very strong principle that both inter-Korean and foreign cooperation will happen once the denuclearization of North Korea happens," he said at the Woodrow Wilson International Center for Scholars.

Kaesong -- a border industrial zone in which South Korean companies enjoyed low-wage labor and the North's government earned badly needed revenue -- was one of the most visible signs of reconciliation that followed the landmark 2000 visit to Pyongyang by Kim Dae-jung, the South's first liberal president.

But South Korea shut the complex down in 2016 under a conservative government as Pyongyang defiantly kept testing nuclear weapons and missiles.

Cho believed that North Korea's young leader Kim Jong Un was more reform-minded than earlier members of the ruling dynasty, who favored self-reliance.

"In order for Chairman Kim to achieve his goal of having a global standard of production, he needs to open his economy," Cho said.

Critics say that North Korea has made no concrete moves to give up its nuclear arsenal despite Moon's three summits with Kim his year and a first-ever meeting in June between the North Korean strongman and US President Donald Trump.

Cho said that a promised landmark visit by Kim to Seoul was still in the planning, although he hinted it could take place later than the end of the year, the timeline set by the two sides.

Cho said that at least two months were needed to plan a proper summit and acknowledged that Kim was wary of expected protests against him in Seoul.

But he said a summit in Seoul would mark "a new breakthrough in history" and demonstrate an unstoppable momentum in inter-Korean relations.

"Chairman Kim's visit to Seoul is something we have agreed on, something we can implement and something that is possible," Cho said.