Seoul also wants a trilateral summit among the countries, or a four-nation meeting that also includes Beijing, to declare a formal end to the 1950-53 Korean War.
The spokesman didn't say whether the team will be meeting with North Korean leader Kim Jong-un.
"Our government believes that an end-of-war declaration is very much needed while we enter a process toward stabilizing peace in the Korean Peninsula through complete denuclearization", said Chung Eui-yong, Moon's national security adviser and the head of the South Korean delegation to Pyongyang, in a news conference on Tuesday. Washington and Pyongyang have been unable to agree on a timeline for North Korea's promise to denuclearize since Kim met U.S. President Donald Trump in June.
"President Trump said he sincerely hoped for the success of the South-North Korea summit in September, not only for an improvement in the South-North Korean relationship but also the implementation of the June 12 U.S".
South Korea's President Moon Jae-in and U.S. President Donald Trump plan to discuss North Korea during the U.N. General Assembly in NY this month, Moon's office and the White House said on Tuesday, amid lacklustre progress on the North's nuclear issues.
Kim added that the war-ending declaration, however, can be easily adopted as long as the related parties have the political will, and it would be reasonable for them to do so to put an end to the state of war.
If Moon fails at his upcoming meeting with Kim, he may face a serious political dilemma: whether to continue to engage the North or join another US -led high-pressure campaign against Pyongyang.
Trump earlier called off a scheduled North Korea trip by his top diplomat, Secretary of State Mike Pompeo, citing what he called a lack of progress in the denuclearization process.
Moon's nightmare may be a return to 2017, when animosity created by the North's barrage of nuclear and missile tests and Trump's responding belligerent tweets raised war fears among South Koreans.
The Pyongyang summit could reveal whether Moon is ready to push ahead with more engagement with the North despite US frustration over North Korea.