North and South Korea signed a declaration on Friday committing to work toward the "complete denuclearization of the Korean Peninsula."

South Korean President Moon Jae-in and North Korean leader Kim Jong Un made the announcement during a high-stakes summit in South Korea on Friday that represented the first time a leader from the North has visited South Korea.

They also agreed to formally end the Korean War of the 1950s.

The meetings come before what is expected to be an even more important and difficult meeting between Kim and President Trump.

In the declaration, the two nations promised to reduce military arms, cease "hostile acts," and agreed to transform the Korean Demilitarized Zone (DMZ) into a "peace zone."

"We solemnly declare to our 80 million Koreans and the world that there will no more war on the Korean peninsula and a new era of peace has begun," a joint statement between Moon and Kim reads.

"It is our urgent historic assignment to put an end to this current abnormal state of ceasefire and establish a peace regime."

Moon and Kim planted a pine tree together at the DMZ on Friday, as the summit began. Near the tree is a plaque with both leader's names and titles and which reads "planting peace and prosperity."

U.S. observers have watched Kim's movements closely and with some anxiety. Just last year, Kim and Trump were engaging in a series of increasingly bellicose messages that had much of the world worried that the countries were edging closer to war.

Since then, Kim has changed tacts, possibly with an eye toward ending crippling sanctions on his country.

Late Friday night, shortly after Kim arrived in North Korea, the U.S. voiced optimism that progress could be made on Pyongyang giving up its nuclear weapons.

"On the occasion of Republic of Korea President Moon Jae-in's historic meeting with North Korean leader Kim Jong Un, we wish the Korean people well. We are hopeful that talks will achieve progress toward a future of peace and prosperity for the entire Korean Peninsula," White House press secretary Sarah Huckabee Sanders said.