Defense Secretary James Mattis said on Friday that there appeared to be more opportunity to unwind tensions with North Korea than at any other point in the more-than-half century since the Korean War.

"I don't have a crystal ball. We are optimistic right now that there's opportunity here that we've never enjoyed since 1950," Mattis said, according to CNN and Pentagon pool reports.

The Defense chief's comments came hours after North Korean leader Kim Jong Un met with South Korean President Moon Jae In for a historic summit, where they pledged to work to remove all nuclear weapons from the Korean Peninsula.

Kim and Moon also pledged to pursue an official end to the Korean War. The conflict began in 1950, and the fighting ceased with an armistice in 1953. But the two countries have technically remained in a state of war since then.

Mattis cautioned against setting preconditions for a treaty officially ending the conflict, and said that negotiations would ultimately be left up to diplomats.

"I think for right now we just have to go along with the process, have the negotiations and not try to make pre-conditions or presumptions about how it's going to go," he said. "The diplomats are going to have to go to work now."

-Updated 5:48 p.m.