The letter comes when the two sides negotiate details of a second meeting between the two leaders. It was flown to Pyongyang and delivered by hand, the source said.
According to the source, North Korea's former spy chief, Kim Yong Chol – one of Pyongyang's best negotiators – may visit Washington this week to finalize details of the upcoming summit.
"We will not relax our watch until the promise to denuclearize the peninsula is maintained and peace is fully institutionalized," Moon added.
After years of isolation, Kim held several diplomatic summits in 2018, meeting Moon, Trump, and Chinese President Xi Jinping. Events so far indicate that 201
Xi and Kim agree, "According to a statement by China's state-run news agency Xinhua, 'to constantly advance the political settlement process of the Korean peninsula.'
The North Korean state media said something Kim said he expressed concern about possible obstacles to the future growth of US-North Korea relations, and Xi "fully complains that North Korea's sensible interests should be resolved."
Last year, North Korea "intensified its international influence and received great support, understanding and passionate welcome from all over the world," stated KCNA.
Kim visited the South Korean capital in December However, this summit was repeatedly delayed as the denuclearization process and talks between Pyongyang and Washington got into trouble.
Asked to attend a press conference last week, Moon said he received a "special" letter from Kim in December explaining why he could not visit the South last year, but said he wanted it see South Korea's leaders more often.
"Our reunion in Pyongyang feels like it happened yesterday, but almost 100 days have passed and the unforgettable year 2018 is coming to an end," Kim said in the letter, an excerpt of which was published by the shared blue house of South Korea.
Although Trump was still Trump's biggest foreign policy achievement, Kim's first meeting with Kim was criticized by some for not pledging North Korea to firm guarantees. Since Pyongyang's commitment to denuclearization and Washington's willingness to take the necessary steps to sign a peace treaty, there are concerns.
Trump stated that sanctions against North Korea will remain "in full force and effect" in the meantime, warning everyone else had been elected US President, "They would be at war."
"You are now in a nice, thick war in Asia with North Korea if I was not elected President," Trump said.