He was speaking ahead of two days of six-party talks set to begin in Beijing after UN nuclear inspectors verified the shutdown of North Korea's Yongbyon reactor.
The reactor produces material that can be turned into weapons-grade plutonium and in February North Korea agreed to close it in return for 50,000 tonnes of heavy fuel oil, which began moving there from South Korea.
North and South Korea, the United States, China, Japan and Russia will now start to explore how to permanently scrap the Yongbyon complex and terminate North Korea's nuclear weapons potential.