TOKYO — South Korean President Moon Jae-in will visit Pyongyang to meet his North Korean counterpart Kim Jong Un on Sept. 18, while the two countries have also agreed to set up a joint liaison office in the North before that date, a top South Korean official said Thursday.

The summit, which will last until Sept. 20, had been planned since last month, but the exact date was set after a team of South Korean envoys traveled to Pyongyang to meet Kim and deliver a letter from Moon on Wednesday.

It will be the third meeting between the two leaders this year, as Moon makes a major effort to improve relations with the North in the hope this will convince Kim scale back or abandon his nuclear arsenal.

It comes despite an impasse in talks between the United States and North Korea, with a planned visit by Secretary of State Mike Pompeo canceled last month.

The summit will discuss the implementation of a joint declaration reached by Moon and Kim when they met in the border village of Panmunjom in April, Director of National Security Chung Eui-yong, who led the team of envoys, said in a statement.

"The discussions at the summit will also be centered around issues on the permanent settlement of peace and common prosperity on the Korean Peninsula as well as, particularly, practical measures to realize denuclearization on the Peninsula," he said.

"Second, Chairman Kim Jong Un reconfirmed his determination to completely denuclearize the Korean Peninsula and expressed his willingness for close cooperation not only with the South but also with the United States in that regard," Chung said.

North and South Korea had agreed to set up the joint liaison office when Moon met Kim in April.

The office will be established in the city of Kaesong in North Korea with resident representatives from both sides, "to facilitate close consultation between the authorities as well as smooth exchanges and cooperation between the people," according to the declaration issued at the end of that April summit.

Kaesong is also the site of an industrial complex jointly developed by both Koreas but largely financed by the South. It was launched in 2004 during a previous bid to improve relations with the North, and enabled South Korean companies to manufacture products using cheaper North Korean labor. But Seoul suspended operations there in 2016 following the launch of a long-range rocket and Pyongyang's fourth nuclear test.

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The Washington Post's Min Joo Kim contributed from Seoul.