The leaders of North and South Korea exchanged letters highlighting their hope for better bilateral relations as South Korean President Moon Jae-in leaves office next month.

The exchange comes amid renewed tension on the Korean Peninsula as Pyongyang has accelerated weapons development and carried out numerous missile tests in recent months.

What did the letters say?

President Moon sent North Korean leader Kim Jong Un a letter on Wednesday urging the North to enter into dialogue with the government of incoming President Yoon Suk-yeol, the presidential office in Seoul said Friday. 

South Korea's conservative President-elect Yoon Suk-yeol takes office on May 10, and has promised to take a tougher stance on North Korean relations. 

Pyongyang's official KCNA news agency said Kim replied on Thursday, and said the letters were a sign of "deep trust" between the two leaders. 

KCNA added that Moon told Kim he would continue to campaign for Korean reunification even after he leaves office. Seoul said that Moon believes that joint declarations for peace after summit meetings in 2018 and a military agreement aimed at mitigating border area clashes would form the foundation for future cooperation.

Moon's spokesperson, Park Kyung-mee, said the South Korean leader also hoped for a resumption of nuclear talks between the United States and North Korea. 

In his reply sent on Thursday, Kim said their "historic" summits gave the people "hope for the future", with the two agreeing that ties would develop if both sides "make tireless efforts with hope," KCNA reported.

"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," KCNA said. 

President Moon staked his legacy on improving ties between the neighbors, spearheading unprecedented meetings between Kim Jong Un and then US President Donald Trump in 2018 and 2019.

Kim and Moon also held three summits in 2018 aiming at promoting peace and reconciliation, but relations have since deteriorated, with Pyongyang warning of destructive action and even demolishing facilities built by southern firms for joint economic projects.

Escalating tensions

President-elect Yoon has said that he is open to dialogue with the North. However, he has rejected "talks for talks' sake" and vowed to bolster Seoul's alliance with Washington.

The incoming leader has hinted at a resumption of their full-scale military exercises to counter the North's nuclear threat.

Last month, Pyongyang launched intercontinental ballistic missiles (ICBMs), breaking a self-imposed 2017 moratorium. Following the launch, there have been increased concerns that the North is preparing to restart nuclear testing.

This week, US President Joe Biden's special envoy for North Korea, Sung Kim, traveled to Seoul for meetings with senior South Korean officials. They agreed on the need for a strong response to counter North Korea's "destabilizing behavior". But Sung Kim added that he is open to sitting down with Pyongyang at any time without preconditions.

see/wmr (AP, Reuters)