South Korean delegates delivered a letter from their president to North Korean leader Kim Jong Un on Wednesday in preparation for a planned summit they hope will maintain the momentum of dialogue on the divided peninsula.

South Korean President Moon Jae-in is due to visit Kim in Pyongyang from Sept. 18 to 20 for the third meeting between the two leaders this year, officials announced Thursday.

The South Korean team also seeks to establish a joint Korean liaison office in the North, officials said. 

The office is a key part of outreach between the two Koreas that began earlier this year and helped open the door for the history-making talks in June between Kim and President Trump.

Trump canceled a planned visit by Secretary of State Mike Pompeo to Pyongyang last month, citing a lack of progress in denuclearization by the North.

Moon, however, considers ongoing dialogue with the North to be the best way to build trust and persuade Pyongyang to abandon or scale back its nuclear weapons program. 

Chung Eui-yong, left, head of South Korea’s presidential National Security Office, talks with North Korean leader Kim Jong Un on Wednesday in Pyongyang. (South Korean Blue House/Getty Images)

Earlier on Wednesday, officials from the South Korean presidential Blue House released photos of Kim meeting the visiting South Korean envoys, with wide smiles all around.

Moon is playing a delicate balancing act, trying to improve relations with the North, while not getting too far ahead of Washington as its parallel peace process with Pyongyang is faltering. 

“President Moon emphasized that now is a critical juncture for the establishment of peace on the Korean Peninsula and that such efforts go in step with complete denuclearization,” the Blue House said in a statement after Moon called Trump. 

At the heart of the impasse between Washington and Pyongyang is a disagreement on which side should make the next move.

North Korea wants the United States to formally declare an end to the Korean War before it takes any genuine steps to open up or scale back its nuclear program, arguing that such a step is vital to defusing tension on the Korean Peninsula and building trust. It says Trump expressed support for such an idea when he met Kim in Singapore.

On Tuesday, North Korea’s Foreign Ministry published a statement on its website arguing that such a declaration should be issued without delay, “as the first process, to manifest the political will to establish the lasting and stable peace regime on the Korean Peninsula.”

Senior U.S. officials are believed to be reluctant to take such a step unless they see concrete action from Pyongyang in dismantling at least part of its nuclear arsenal.

North Korea wrote to Pompeo last month, warning that the peace process was faltering and telling him not to come to Pyongyang unless he was willing to bring further concessions, officials have said.

Before the latest setback, Moon had spoken optimistically about his planned September summit with Kim and promised that the pair would take an “audacious step” toward the signing of a peace treaty and the complete denuclearization of the Korean Peninsula. 

Last month, he also expressed hope that groundbreaking ceremonies to establish road and rail links between the two Koreas could take place before the end of the year, and he set out an ambitious vision of long-term economic integration between the neighbors.

Koh Yu-hwan, a policy adviser at South Korea’s National Security Office and professor of North Korean studies at Dongguk University, said Seoul could not simply sit on its hands amid the impasse between Pyongyang and Washington.

“If inter-Korean relations also stagnate, the diplomatic momentum could be lost,” he said in an interview. “Making headway on inter-Korean dialogue can possibly lead to progress on the denuclearization front.”

Kim reported from Seoul.