SEOUL, South Korea (AP) The leaders of the rival Koreas have exchanged letters expressing hope for improved bilateral relations, which plummeted in the past three years amid a freeze in nuclear negotiations and North Korea s accelerating weapons development.

North Koreas state media said Friday that leader Kim Jong Un received a personal letter from outgoing South Korean President Moon Jae-in on Wednesday and replied on Thursday with his own letter appreciating Moons peace efforts during his term.

Pyongyangs official Korean Central News Agency said their exchange of letters showed their deep trust. Moons office also confirmed that he exchanged letters with Kim but didnt immediately say what was said.

The exchange of letters came amid heightened tensions created by a series of North Korean weapons tests this year, including its first flight-test of an intercontinental ballistic missile since 2017 in March, reviving a nuclear brinkmanship aimed at forcing the U.S. to accept it as a nuclear power and remove crippling tensions.

South Koreas military has also detected signs that North Korea is rebuilding tunnels at a nuclear testing ground it partially dismantled weeks before Kims first meeting with then-U.S. President Donald Trump in June 2018, a possible indicator that the country is preparing to resume nuclear explosive tests.

Moon met Kim three times in 2018 and lobbied hard to help set up Kims meetings with Trump. But the diplomacy never recovered from the collapse of the second Kim-Trump meeting in 2019 in Vietnam, where the Americans rejected North Koreas demands for major sanctions relief in exchange for dismantling an aging nuclear facility, which would have amounted to a partial surrender of its nuclear capabilities.

Kim has since vowed to bolster his nuclear deterrent to counter gangster-like U.S. pressure and sped up his weapons development despite limited resources and pandemic-related difficulties.

North Korea also severed all cooperation with Moons government while expressing anger over U.S.-South Korea military exercises and Seouls inability to wrest concessions from Washington on its behalf.

The KCNA said that Moon, whose term ends next month, said in his letter to Kim that he will continue to support efforts for reunification between the war-torn rivals based on their joint declarations for inter-Korean peace issued after their meetings in 2018.

North Korea now faces a new South Korean leader who could possibly take a harder line toward Pyongyang. Conservative South Korean President-elect Yoon Suk Yeol, who takes office on May 10 after narrowly winning the March 9 election, has rejected pursuing talks for talks sake with North Korea and vowed to bolster Seouls alliance with Washington to counter the Norths nuclear threat.