The secretary of state was unable to specify a time frame, but said he hopes it will occur soon.
The North Korean leader is slated to meet with President Trump in Hanoi later this week.
Trump met for 90 minutes Friday with North Korean envoy Kim Yong Chol to discuss denuclearization and a second summit.
Pyongyang's statement raises further doubts on whether leader Kim Jong Un will ever relinquish his arsenal.
"All agreements aimed at nuclear disarmament ... must be preserved, for the sake of preserving life on earth," the former Soviet leader said.
He's working to set up a second summit between President Donald Trump and North Korean leader Kim Jong Un.
The two sides offered mixed messages on North Korean denuclearization.
There's nothing novel about suspending joint military exercises, and there's no guarantee it will make a difference.
Experts say the U.S. needs to formulate a concrete roadmap to achieve denuclearization in the Korean peninsula.
One expert called the agreement a “warm and fuzzy pile of generalities and old news.”
"That is about the stupidest and most dangerous statement I have ever heard an American president make."
The nuclear powers have not kept their part of the Nuclear Non-Proliferation Treaty bargain. While the US and Russia have dismantled many of their nuclear weapons since the end of the Cold War, they retain thousands of them, enough to destroy the world many times over.