South Korea's SEOUL (AP) — The opposing Koreas' presidents exchanged letters in which they expressed optimism for improving bilateral ties, which have deteriorated in recent years due to a halt in nuclear talks and North Korea's rapid weapons development.

        Kim Jong Un got a personal letter from outgoing South Korean President Moon Jae-in on Wednesday, according to North Korean official media, and responded on Thursday with his own letter praising Moon's peace efforts throughout his term. Their exchange of letters, according to Pyongyang's official Korean Central News Agency, demonstrated their "deep confidence."

        Experts believe North Korea's announcement of the letters, which comes as Kim is rumored to be planning a nuclear test and other major provocations, is intended to divide public opinion in South Korea and discourage Seoul's new government from taking a tough stance toward Pyongyang after taking office in May.

        Moon assured Kim, according to KCNA, that even when he leaves office next month, he will continue to advocate for Korean reunification, basing his efforts on their joint declarations for peace released following their summit talks in 2018.

        "Inter-Korean ties would strengthen and grow as desired and anticipated by the (Korean) country if the (North and South) undertake relentless efforts with optimism," Kim and Moon agreed, according to KCNA. 

        Moon's administration verified the letter exchange quickly after KCNA's story, but took hours to release its version of events, implying that the North did not coordinate with Seoul before revealing the exchange. The story by KCNA was not published in the North's official Rodong Sinmun newspaper, which is read by the North's domestic readership, indicating that the message was meant for the South.

        Moon acknowledged setbacks in inter-Korean relations in his letter to Kim, according to Seoul, but insisted that their aspirational pledges for peace during their summits in 2018 and an accompanying military agreement aimed at defusing border area clashes remain relevant as a foundation for future cooperation.

        Moon's spokesperson Park Kyung-mee said Moon expressed hope for a resumption of nuclear talks between Washington and Pyongyang, as well as for Kim to pursue cooperation with Seoul's next government, led by conservative President-elect Yoon Suk Yeol.

        While delivering a letter to the North's leader as the South's departs office is a formality, expert Cheong Seong-Chang of the South's private Sejong Institute believes the North made the personal correspondence public in order to sow discord in the country ahead of a government transition.

        "Given signs that North Korea is preparing for its seventh nuclear test, it's debatable whether President Moon's letter to Chairman Kim to offer his cordial wishes was acceptable," Cheong added.

        Yoon, who enters office on May 10, has slammed Moon's foreign policy, calling it "subservient" to North Korea and vowing to avoid "talks for the sake of talks." He has promised to bolster South Korea's defense in tandem with its partnership with the US, which he claims would involve improving preemptive strike capabilities and anti-missile defense systems to prevent North Korean threats.

        Tensions on the Korean Peninsula have risen since North Korea conducted a series of weapons tests this year, including its first flight-test of an intercontinental ballistic missile since 2017, reviving the nuclear brinkmanship aimed at forcing the US to accept it as a nuclear power and lift crippling sanctions.

        South Korea's military has also discovered signs that North Korea is reopening tunnels at a nuclear testing site it had partially dismantled weeks before Kim's first meeting with then-President Donald Trump in June 2018, possibly indicating that the country is planning to resume nuclear explosive tests.

        Moon met Kim three times in 2018 and worked hard to help set up Kim's talks with Trump, staking his single presidential term on inter-Korean reconciliation. The diplomacy, however, never recovered from the failure of the second Kim-Trump meeting in Vietnam in 2019, when the Americans rejected North Korea's demands for major sanctions relief in exchange for the dismantling of an aging nuclear facility, which would have amounted to a partial surrender of the country's nuclear capabilities.

        Since then, Kim has pledged to strengthen his nuclear deterrence in response to "gangster-like" US pressure and has accelerated his weapons development despite limited resources and pandemic-related challenges.

        North Korea also cut off all ties with Moon's administration, expressing displeasure with the United States' continued military exercises with South Korea, which had been curtailed in recent years to promote diplomacy with the North, as well as Seoul's inability to wrest concessions from Washington on its behalf.

        North Korea is expected to expand its weapons displays in the next weeks or months, according to analysts, in order to compel a response from the Biden administration, which has been preoccupied with Russia's war in Ukraine and its competition with China.

        Sung Kim, Biden's special envoy for North Korea, met with senior South Korean officials this week and said they agreed on the necessity for a forceful reaction to counter North Korea's "destabilizing actions."

        After years of keeping a friendly tone, Moon's administration expressed its opposition to North Korea's nuclear tests more forcefully this year, slamming Kim's regime for lifting its self-imposed moratorium on long-range missile testing and advocating a return to talks.

        Seoul has also accused North Korea of demolishing South Korean-owned infrastructure at the North's Diamond Mountain resort, where the two countries collaborated on tours until 2008. The coronavirus epidemic delayed the construction, but Kim termed the South Korean facilities there "shabby" and ordered them dismantled in 2019.