It was sent days before Kim delivers his annual New Year's Day speech, which will be examined for signs of whether the US and North Korea will continue with their rapprochement or drift back toward confrontation.
The group was among at least a dozen civic group, known collectively as the "Paektu Praise Committee" which have become an unofficial welcome group for Kim if he visits Seoul.
The timing of the speech is unclear, since North Korea rarely provides advance notice about Kim's schedule.
"In his letter, Chairman Kim sent warm end-of-the-year greetings and said the leaders of the two Koreas should move forward together in the new year for peace and prosperity on the Korean Peninsula".
With limited negotiations having been made between the USA and North Korea in recent months, it makes sense that Kim would be trying to cut through the bureaucracy with direct leader-to-leader communications. In his meetings with Moon and Trump, Kim signed on to vague statements calling for a nuclear-free Korean Peninsula without describing when or how it would occur.
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An image of North Korean leader Kim Jong Un and South Korean President Moon Jae-in at a park near the presidential Blue House in Seoul.
Kim added that he was sorry his plan to visit Seoul later this year - in what was to be their fourth meeting of 2018 - did not take place as agreed at their third summit in Pyongyang in September.
In the letter, sent to mark the end of the year and underline a recent thaw in ties between the two Koreas, Kim "expressed a strong determination to visit Seoul while watching the future situation", Moon's spokesman, Kim Eui-kyeom, told reporters. Officials in neighboring countries follow the speeches closely to obtain overall information about the country and how it will act on diplomatic issues such as its nuclear weapons program.
Kim Jong-un has penned a rare letter to South Korean President Moon Jae-in agreeing to more summits in the New Year. and signaling he will eventually come down to Seoul.
Post-summit nuclear talks between Washington and Pyongyang quickly settled into a stalemate as the countries struggled between the sequencing of the North's disarmament and the removal of USA -led global sanctions against the North.
Denuclearizing the peninsula was the focus of the summit in Singapore last June between Kim and Trump.