“A U.S. delegation is in ongoing talks with North Korean officials at Panmunjom,” State Department spokeswoman Heather Nauert said in a statement, referring to the truce village in the demilitarized zone between the Koreas. “We continue to prepare for a meeting between the president and North Korean leader Kim Jong Un.”

Nauert provided no further details. The Washington Post reported that Sung Kim, a former U.S. ambassador to South Korea, is leading the delegation and met Sunday with North Korea’s vice foreign minister, Choe Son Hui.

Trump told reporters on Saturday night that meetings were taking place “as we speak” in an location he didn’t specify to advance preparations for the historic meeting he abruptly canceled last week — in a sharply-worded letter to Kim — due to “open hostility” from North Korea.

“We’re doing very well in terms of the summit with North Korea,” Trump said Saturday night. “We’re looking at June 12 in Singapore. That hasn’t changed, and it’s moving along pretty well. So we’ll see what happens.”

Kim, Moon Talk

Sung, a South Korean born diplomat, is a former nuclear negotiator and current U.S. ambassador to the Philippines. Allison Hooker, a Korea specialist on the National Security Council, is reportedly also part of the team. The meetings are expected to go through Monday and Tuesday, the newspaper reported.

Trump’s remarks came a day after South Korean President Moon Jae-in held a surprise two-hour meeting with Kim on the border in a bid to keep the Trump summit on track. Moon said on Sunday that Kim requested the meeting, only the fourth ever by leaders of the two countries since the Korean War.

“Chairman Kim clearly appealed once again that his intent to completely denuclearize the Korean Peninsula is firm,” Moon said. “What’s unclear for Chairman Kim, in my opinion, is not his willingness for denuclearization but whether he can certainly trust the U.S. saying that it’ll end hostile relations and guarantee the security of his regime after his denuclearization.”

Separately, the White House said Saturday that an advance team will travel to Singapore, the planned site of the summit, to continue preparations — just in case.

South Korea is reviewing ways to address North Korea’s security concerns, including turning the current armistice into a peace agreement, a senior Moon administration official said on Sunday. Moon reiterated a goal to hold a trilateral summit with both Trump and Kim to officially end the Korean War if their meeting is successful.

The second meeting between Kim and Moon in as many months reflects urgency among both men to maintain momentum for diplomacy. Since taking power last year, Moon has sought to facilitate dialogue between Trump and Kim to avoid the possibility of a devastating military conflict on the Korean Peninsula.

North Korea’s state news agency, KCNA, said the Korean leaders had agreed to “high-level” talks between the two countries on June 1. “They shared the opinion that they would meet frequently in the future to make dialogue brisk and pool wisdom and efforts,” KCNA said.

Main Dispute

The main dispute between the U.S. and North Korea boils down to how fast Kim should give up his weapons, and what he’ll get in return.

North Korea rejected outright calls from U.S. National Security Adviser John Bolton to follow the Libya model of quickly giving up its nuclear weapons before it gets anything in return. Libyan dictator Moammar Qaddafi was killed in an uprising several years later.

Moon on Sunday dodged a question on whether Kim clearly mentioned if he would agree to the U.S. demand for complete, verifiable, irreversible denuclearization.

“If North Korea and the U.S. are to have a summit, then their summit is possible only after they confirm each other’s intention on that regard,” Moon said. “I’d like to say that the fact that North Korea and the U.S. agreed to have a summit and working-level talks indicates that the U.S. has already confirmed the North’s intentions.”

Keeping Nukes

Michael Hayden, who led the Central Intelligence Agency and the National Security Agency under Republican and Democratic presidents, said on ABC’s “This Week” that a summit is “more rather than less likely” to happen. But he and Republican Senator Marco Rubio agreed it’s unrealistic to expect Kim to give up his nuclear weapons.

“I remain convinced that he does not want to denuclearize, in fact he will not denuclearize,” Rubio, a member of the Senate Foreign Relations and Intelligence committees. “But he wants to give off this perception that he’s this open leader, that he’s peaceful, that he’s reasonable.”

Rubio called Kim’s willingness to release U.S. hostages and destroy a nuclear test site “all a show.”

Hayden said the most optimistic scenario for the summit is to reach an agreement to keep making the Korean peninsula more stable and less prone to war. He said Kim has already made great progress on nuclear and ballistic missile technology.

“He’s kind of gotten where he needs to be,” Hayden said. “He’s willing to park the car for now and then go talk.”

Denuclearization Flexibility

The White House has signaled flexibility over the details of denuclearization, with Press Secretary Sarah Huckabee Sanders saying earlier this month that the administration will follow the “President Trump model.” North Korea seized on that in a statement on Friday calling for talks with the U.S.

North Korea “inwardly highly appreciated” Trump for agreeing to the summit, and hoped the “Trump formula” would help lead to a deal between the adversaries, First Vice Foreign Minister Kim Kye Gwan said in a statement Friday urging the resumption of talks.

Trump’s letter to Kim canceling the planned June 12 summit didn’t rule out a meeting in the future, said a person familiar with the administration’s thinking. The person, who asked not to be identified discussing internal matters, said the “maximum pressure” campaign to strangle North Korea’s economy is working, and Kim’s regime will have to come to the table eventually.

Secretary of State Mike Pompeo tweeted on Saturday to “Stay Focused. It’s about the outcome. It’s about keeping Americans and the world safe.”