North Korean leader Kim Jong Un told a team of South Korean envoys that he continues to trust President Trump and said he hoped to achieve the denuclearization of the Korean Peninsula while Trump is in office, the chief envoy said Thursday.

Trump responded on Twitter by expressing his appreciation.

“Kim Jong Un of North Korea proclaims ‘unwavering faith in President Trump,’” the U.S. president tweeted. “Thank you to Chairman Kim. We will get it done together!”

But there also was a reminder of the current impasse in negotiations.

North Korean media repeated the country’s demand that the United States make the next move by formally declaring an end to the Korean War, which concluded in 1953 with an armistice but not a peace treaty. 

The North insists Trump promised such a declaration when he met Kim in Singapore in June. But it is a move that Washington is reluctant to make, fearing that it could ultimately throw into question the continued presence of U.S. troops in South Korea. 

The South Korean envoys delivered a letter from President Moon Jae-in, as well as a message from Trump, who spoke to Moon by telephone earlier in the week. 

The two sides agreed that a planned summit between the leaders of both Koreas would take place in Pyongyang on Sept. 18-20, and they pledged to open a joint liaison office in the North before then.

“I have big expectations for the upcoming inter-Korean summit,” Moon told officials on Thursday, according to the presidential Blue House. “I also have expectations for complete denuclearization of the Korean Peninsula, and for talks between North Korea and the United States to be accelerated as well.”

In Wednesday’s meeting, North Korea’s Kim expressed frustration with skepticism in some parts of the international community about his commitment to denuclearize, according to Chung Eui-yong, South Korea’s director of national security and the leader of the team of envoys.

The North Korean leader also pointed to the dismantling of the Punggye-ri nuclear test site and Dongchang-ri missile launch facility as evidence of his commitment to end nuclear testing permanently, Chung said. And he asked for a message to be delivered to Trump. 

That message will very probably contain an appeal for the United States to formally declare an end to the war, something North Korea says is vital to building trust and ending decades of hostility.

Kim said such a declaration would not imply a withdrawal of U.S. troops or a weakening of the U.S.-South Korean military alliance, Chung added.

“Chairman Kim said that although the dialogue between the U.S. and North Korea is experiencing some difficulties, his trust in President Trump continues, especially at times like this,” Chung told a news conference the day after his return. 

He added that Kim pledged to “to end 70 years of hostile relations with the United States, improve the bilateral relationship and fulfill denuclearization before the end of President Trump’s first term.”

An end-of-war declaration is seen as only a first step toward a full peace treaty, which in theory would involve the denuclearization of the Korean Peninsula and normalization of diplomatic relations between Pyongyang and Washington, diplomats say.

On Thursday, North Korea’s Rodong Sinmun newspaper said the Trump administration must discard its “stubborn” stance that the North must denuclearize first before the United States agrees to a peace treaty. 

It said North Korea has shown “goodwill and generosity” through actions such as returning the remains of some U.S. servicemen who died in the Korean War and dismantling the nuclear test site at Punggye-ri but that the United States has failed to respond with corresponding measures to improve relations.

The summit later this month will be the third meeting between leaders of the two Koreas this year, as Moon makes a major effort to improve relations with the North in the hope that this will persuade Kim to scale back or abandon his nuclear arsenal. 

It will discuss the implementation of a joint declaration reached by Moon and Kim when they met in the border village of Panmunjom in April.

Harry Kazianis, director of Defense Studies at the Center for the National Interest in Washington, said he felt the envoys’ visit could not have gone any better.

“In fact, I would not rule out a peace declaration being signed by all parties this year,” he added. “If Trump wants a legacy-building moment abroad, especially at a time when his administration has problems back home, ending the Korean War could be it.” 

Min Joo Kim reported from Seoul.