Kim Jong Un's "Thank You" Letter to South Korea's Moon After Turbulent Ties

North Korean leader Kim Jong Un exchanged letters with outgoing South Korean President Moon Jae-in to thank him for his efforts at rapprochement, just days before a hawkish new leader takes power in Seoul and vows to pursue a tough line with Pyongyang.

After receiving a letter from the South Korean president on Wednesday, Kim responded with a letter that expressed appreciation for "the pains and effort taken by Moon Jae-in for the great cause of the nation until the last days of his term of office," North Korea's official media reported. South Korea is expected to brief on the letters later Friday.

"The exchange of the personal letters between the top leaders of the north and the south is an expression of their deep trust," the state's Korean Central News Agency reported Friday, adding Moon expressed his desires to Kim to work on improving inter-Korean ties even after his retirement.

The letters mark a closing chapter in a turbulent relation between Moon and Kim, who held three summits in 2018 that produced an agreement to reduce military tensions on the border and paved the way for historic talks between Kim and then U.S. President Donald Trump. After the discussions with Trump faltered, North Korea branded Moon a meddlesome mediator, ignored his calls for talks and blew up a $15 million liaison office north of the border that was one of the South Korean leader's biggest achievements.

President-elect Yoon Suk Yeol, a conservative who takes office on May 10, has said he may scrap the military deal reached by Moon and Kim. He also said during his campaign that he would be ready to launch a preemptive strike on the neighbor to the north to stop an impending attack. Kim Yo Jong, the powerful sister of North Korea's leader, issued a stinging rebuke of the policy.

Ties between the two Koreas have typically cooled when a conservative leads South Korea and North Korea has already ratcheted up tensions before Yoon takes over. Over the past several months, it has rolled out a new array of weapons designed to strike South Korea, and in March, it launched its first intercontinental ballistic missile since 2017.

Satellite imagery indicates Pyongyang has been restoring tunnels at the Punggye-ri site where it conducted all six of its previous nuclear tests, in what could be the harbinger of an imminent test of an atomic device. It also appears North Korea could stage a military parade as soon as next week to show off its weaponry.

Although North Korea still languishes under a range of United Nations sanctions, it has continued to roll out an array of new missiles that would require smaller, more advanced warheads to pose a credible deterrent to the U.S. Such weapons could increase Kim's leverage if he decides to return to nuclear disarmament talks and ease the sanctions choking the economy.