North Korean leader Kim Jong Un has exchanged letters with South Korea’s outgoing President Moon Jae-in and thanked Moon for his efforts to improve relations, state media KCNA reported on Friday (April 22).

Moon sent a letter on Wednesday and promised continued efforts to help lay the foundation for unification based on the joint declarations reached at their summits in 2018, KCNA said.

Kim said in his reply on Thursday that their “historic” summits in 2018 gave “hope for the future” to the people, and the two agreed that the ties would develop if both sides “make tireless efforts with hope.”

“Kim Jong Un appreciated 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,” the official KCNA news agency said, adding the exchange of letters was an “expression of their deep trust.