SEOUL — As senior U.S. and North Korean officials worked toward reviving an aborted meeting between Kim Jong Un and President Trump, South Korea on Thursday expressed interest in a three-way summit in Singapore that would add South Korean President Moon Jae-in to the mix.

South Korean officials said a three-way meeting would materialize only if it was supported by Pyongyang and Washington.

The progressive South Korean president has said he hopes for such a meeting, which perhaps could take place immediately after the scheduled June 12 summit in Singapore. A meeting of the three countries’ leaders could provide an opening for Moon to advance a long-sought goal: a peace accord that formally ends the Korean War.

Political allies and experts say Moon’s government views such a declaration as an incentive to North Korea to agree to denuclearization. And it’s a personal issue to Moon, the son of North Korean refugees, they said. 

“If there is an official declaration of the end of the Korean War, then there would be a route to achieving peace on the peninsula, so he [Moon] wants to declare the end of the war as soon as possible,” said Kim Yong-hyun, a professor of North ­Korean studies at Dongguk University in Seoul. 

But the Trump administration is currently divided on whether agreeing to a peace treaty at the outset of the talks would give away a significant concession too early in the negotiations, said two people familiar with the matter, who, like others, spoke on the condition of anonymity to discuss negotiation strategies. That concern could create a potential rift with Seoul, which wants to remain involved in the negotiations in the long term but doesn’t want to be seen as inserting itself improperly too early. 

A senior administration official said that both Moon and Japan’s prime minister, Shinzo Abe, had been eager to play a role in the talks, but that the goal as of last week was to keep the initial meetings to just Trump and Kim.

“The president is trying to keep them at arm’s length,” the official said of both Abe and Moon. Trump’s theory is that he can better build rapport with Kim and offer him the reassurance he needs in a one-on-one negotiation.

The move reflects the belief in the White House that the success of the summit hinges on Trump’s skills as a dealmaker. To that end, U.S. officials have been intent on keeping the brief they are presenting to Trump short and focused on the security and economic guarantees he could offer to the North Koreans. Efforts from the State Department and elsewhere to add on to the president’s talking points have been brushed back.

The message has been “don’t add extraneous stuff to the discussion,” the official said. “The president’s desire is to keep it very, very focused.”

If the United States and North Korea do decide to extend an invitation, Moon could travel to Singapore as early as the afternoon of June 13, according to people familiar with discussions. This would allow Trump and Kim to share the spotlight at their June 12 summit and permit Moon to be in Seoul for a part of June 13, when local elections will be held in South Korea, they said. 

South Korea sent an official to Singapore for planning in advance of the annual Shangri-La Dialogue conference, which starts Friday. Those preparations could also support a possible three-way summit with Kim and Trump, according to a person familiar with the visit.

At the April 27 inter-Korean summit between Moon and Kim, the two leaders agreed to “actively pursue” three-way talks with the United States or four-way talks, adding China, to turn the 1953 armistice into a permanent peace treaty. In the Panmunjom Declaration, which Moon and Kim signed, they agreed that “bringing an end to the current unnatural state of armistice and establishing a robust peace regime on the Korean Peninsula is a historical mission that must not be delayed any further.” 

South Korean officials are now watching to see how pre-summit discussions between the United States and North Korea unfold to gauge whether a three-way summit would be plausible.

A State Department spokesman declined to say whether Washington supports declaring an end to the Korean War as an early carrot to nurture negotiations with Pyongyang: “We are not going to get out ahead of ongoing discussions.”

A spokesman for the National Security Council declined to comment on ongoing diplomatic talks.

Some analysts are skeptical that agreeing to a peace treaty would make a significant difference. Chun Yung-woo, a former South Korea national security adviser and nuclear negotiator with the North, said the armistice signed 65 years ago is de facto a declaration of the end of the war. 

An official declaration at a trilateral meeting would be “nothing more than a political commitment to concluding a peace treaty as part of the de­nuclearization deal. Nor can it play a role in closing the gap on denuclearization between the U.S. and North Korea,” Chun said.

“I am not sure what meaningful contribution President Moon can make in Singapore,” he said. “Even though he may wish to share the credit for any deal coming out of the U.S.-N.K. summit with his presence, he runs the risk of being treated like an odd man out eager to be part of the show.”

Declaring an end to the war could serve as the first ceremonial step to normalizing North Korean relations with the United States and open the way to a peace treaty under which U.S. troops might one day leave the peninsula, said Duyeon Kim, visiting senior research fellow at the Korean Peninsula Future Forum in Seoul. 

Moon said in his remarks earlier in the week that he hoped to pursue a three-way meeting if the U.S.-North Korea summit goes ahead. But since then, the presidential Blue House has tried to quash speculation about his plans.

“The nuclear issue structurally — by itself and the characters [involved] — should be bilateral between United States and North Korea,” Kim Joon-hyung, a foreign policy adviser to Moon, said. “But the whole peace process, we can get in. We can be in the driver’s seat . . . . What President Moon thinks is, after we pass [bilateral] obstacles we’ll be much more active. So he’s waiting and waiting.”

And he may end up waiting longer.

Given that significant differences remain between the United States and North Korea over fundamental issues surrounding denuclearization, it’s too soon to tell whether a three-way meeting is possible, Duyeon Kim said. 

“It’s currently an ambitious endeavor, but we’ll have to wait and see,” she said.

Also on Thursday, Russian foreign minister Sergei Lavrov arrived in Pyongyang for talks with his North Korean counterpart, Ri Yong Ho.

The Korean issue will not be fully settled until sanctions against North Korea are lifted, Lavrov told reporters in Pyongyang. He called for a phased easing of the sanctions. 

“Denuclearization cannot be immediate, so there should, of course, be certain stages and measures taken at every stage to meet each other halfway,” he said.

Hudson reported from Singapore. Greg Jaffe in Washington and Natalya Abbakumova in Moscow also contributed to this report.