SEOUL, South Korea — Kim Jong Un expressed faith in an increasingly embattled President Donald Trump's efforts to settle a nuclear impasse but demanded that his "goodwill measures" be met in kind, South Korean officials said Thursday after meeting with the North Korean leader.

The trove of comments from Kim, including his commitment to a nuclear-free Korean Peninsula and to the suspension of all future long-range missile tests, was filtered through the liberal South Korean government, which is keen on keeping engagement alive, and also through Kim's propaganda specialists in Pyongyang.

But, even in their indirect form, each statement will be parsed for clues about the future of nuclear diplomacy amid a growing standoff with the United States on how to proceed with negotiations meant to settle a dispute that had many fearing war last year.

Only hours before they briefed the media in Seoul, a South Korean delegation returned from talks with Kim where they set up a summit for Sept. 18-20 in Pyongyang between the North Korean leader and South Korean President Moon Jae-in, their third meeting since April.

South Korean officials said they forwarded a message from Trump to Kim during their meeting and would send a separate message from Kim to Trump later Thursday. The officials wouldn't discuss the content of the messages.

Some of Kim's reported comments — his commitment to a nuclear-free Korea, for instance — were reiterations of past stances, but there will be sharp interest in whether they push negotiators back to diplomacy after the recriminations that followed Kim's meeting in June with Trump in Singapore.

The impasse between North Korea and the United States, with neither side seemingly willing to make any substantive move, has generated widespread skepticism over Trump's claims that Kim will really dismantle his nuclear weapons program. Despite Kim's repeated denuclearization commitments, recent satellite photos have indicated his weapons factories were still operating to produce fissile materials to make nuclear weapons.

In his meeting with the South Koreans, Kim seemed to go out of his way to praise Trump, while also noting exasperation.

"Chairman Kim Jong Un has made it clear several times that he is firmly committed to denuclearization, and he expressed frustration over skepticism in the international community over his commitment," Chung Eui-yong, Moon's national security adviser and the head of the South Korean delegation to Pyongyang, told reporters in Seoul. "He said he's pre-emptively taken steps necessary for denuclearization and wants to see these goodwill measures being met with goodwill measures."

Chung reported Kim as saying that work to dismantle the only missile engine test site in the country "means a complete suspension of future long-range ballistic missile tests." Kim said he'd take "more active" measures toward denuclearization if his moves are met with corresponding goodwill measures, and that he wanted to settle the matter within Trump's first term, Chung said.

Kim told Chung he still had faith in Trump despite diplomatic setbacks, and emphasized that he has not once talked negatively about Trump to anyone, including his closest advisers.

Kim Jong Un of North Korea proclaims “unwavering faith in President Trump.” Thank you to Chairman Kim. We will get it done together! — Donald J. Trump (@realDonaldTrump) September 6, 2018

Kim also said an end-of-war declaration that Seoul and Pyongyang have been pushing Washington to sign off on wouldn't weaken the U.S.-South Korean alliance or lead to the withdrawal of the 28,500 U.S. troops stationed in South Korea to prevent North Korean attack, according to Chung.

The summit later this month between Kim and Moon, the driving force behind the current diplomacy, will be a crucial indicator of whether larger nuclear negotiations with the United States will proceed.

Moon is seen as eager to keep the diplomacy alive in part so that he can advance his ambitious engagement plans with the North, which would need U.S. backing to succeed.

While pushing ahead with summits and inter-Korean engagement, Seoul is trying to persuade Washington and Pyongyang to proceed with peace and denuclearization processes at the same time so they can overcome a growing dispute over the sequencing of the diplomacy.

Seoul and Pyongyang both want a declaration to formally end the 1950-53 Korean War. U.S. officials have insisted that a peace declaration, which many see as a precursor to the North eventually calling for the removal of all U.S. troops from the Korean Peninsula, cannot come before North Korea takes more concrete action toward abandoning its nuclear weapons. Such steps may include providing an account of the components of its nuclear program, allowing outside inspections and giving up a certain number of its nuclear weapons during the early stages of the negotiations.

The Korean War ended with an armistice, leaving the peninsula technically still at war. Moon has made an end-of-war declaration an important premise of his peace agenda with North Korea.

While an end-of-war declaration wouldn't imply a legally binding peace treaty, experts say it could create political momentum that would make it easier for North Korea to steer the discussions toward a peace regime, diplomatic recognition, economic benefits and security concessions.

After their June summit in Singapore, Trump and Kim issued a vague statement about a nuclear-free peninsula without describing when and how it would occur. Post-summit nuclear negotiations between Washington and Pyongyang were rocky and quickly settled into a stalemate.

Trump called off a planned visit to North Korea by Secretary of State Mike Pompeo last month, citing insufficient progress in denuclearization.