The leaders of North and South Korea exchanged “warm” letters ahead of the New Year, pledging to work toward peace and prosperity in 2019.

The diplomatic exchange follows a year of détente between the two neighboring powers, which are technically still at war.

North Korean leader Kim Jong Un wrote to South Korean President Moon Jae-in expressing his hope that the pair meet “often” in 2019 to work towards denuclearization on the Korean peninsula, South Korea’s presidential office said Sunday.

Kim also said he regretted not being able to visit the South Korean capital Seoul in 2018 as planned but hoped to reorganize the trip for next year.

The two Korean leaders have held three summits in 2018, including Moon’s visit to the North Korean capital, Pyongyang, which marked the first time a South Korean leader had visited the city in 11 years.

Kim said the pair had achieved “bold and realistic measures” in 2018 which had succeeded in making our nations “depart from fear of war and the military tension.”

Responding to the letter, Moon said he welcomed Kim’s intention to work together.

“There will still be a lot of difficulties ahead,” Moon said. “However, our hearts will become more open if we put in that much effort. There’s no change in our heart about welcoming Chairman Kim [to the South].”

The past year has seen the rivals take important steps toward peace and friendlier diplomatic relations.

Prior to Moon’s election in 2017, the two Koreas traded apocalyptic threats and deadly shell fire rather than warm words. As recently as last September, Pyongyang warned it could wipe out the South in a nuclear strike.

Moon has been "a key driver of this diplomacy since its inception," Abraham Denmark, a director at the Woodrow Wilson International Center for Scholars recently told NBC News.

He's proved to be a skilled and effective navigator among Kim and the leaders of the U.S., China and Japan, Demark added.

Since Moon’s election, the North and South have pledged to work toward ending the Korean War and to avoid military provocations. They have also allowed families divided by the war brief and emotional reunions, and held the promise of future economic ties.

The détente between the two powers has run in parallel with the U.S.-North Korean negotiations.

In June, Kim and President Donald Trump pledged to "work toward complete denuclearization of the Korean Peninsula" at a historic summit in Singapore.

But their joint declaration was vague and has been widely dismissed as almost meaningless.

The pair have since made little progress and have struggled to reschedule a high-level meeting which was abruptly called off in November.

Earlier this month, the U.S. slapped sanctions on three high-profile North Korean officials over alleged human rights abuses. In response, Pyongyang warned of a return to the "exchanges of fire" of last year.

Trump and Kim are due to hold a second summit in 2019 but Moon’s office did not reveal whether Kim made any comments on the subject in his exchange with the South Korean president.

The end of year exchange between the Korean leaders comes days before Kim is expected to address North Koreans in a New Year’s speech that is traditionally used to announce major policy decisions and goals.

Last year, Kim called on the research sector and rocket industry to “mass-produce nuclear warheads and ballistic missiles." In contrast, Yonhap reported Sunday that Kim will likely tamp down his fiery rhetoric this year in order to not provoke the United States.