U.S. officials arrived in North Korea to continue planning for the possible June 12 summit in Singapore between the two countries, President Donald Trump said Sunday.

“Our United States team has arrived in North Korea to make arrangements for the Summit between Kim Jong Un and myself. I truly believe North Korea has brilliant potential and will be a great economic and financial Nation one day,” the President tweeted.

Earlier, State Department spokesperson Heather Nauert said both countries are holding talks concerning the summit at the Demilitarized Zone (DMZ).

“A U.S. delegation is in ongoing talks with North Korean officials at Panmunjom. We continue to prepare for a meeting between the President and North Korean leader Kim Jong-un,” Nauert said in a statement.

“In addition to those talks, White House spokeswoman Sarah Sanders said a “pre-advance team” left for Singapore – where the summit has been expected to take place – on Sunday morning to work on logistics. Earlier on Sunday, South Korean President Moon Jae-in said he and North Korea’s Kim had agreed during a surprise meeting on Saturday that the North Korea-U.S. summit must be held,” Reuters reports.

After welcoming home Joshua Holt, a U.S. citizen rescued from Venezuela, President Trump signaled optimism about meeting the North Korean leader.

“I think people want to see if we can get the meeting and get something done,” the President told reporters.

“We got that done and we can be successful in the denuclearization of the Korean Peninsula, that would be a great thing for North Korea, it would be a great thing for South Korea, it would be great for Japan, it would be great for the world, it would be great for the United States, it would be great for China.”

“A lot of people are working on it. It’s moving along very nicely,” Trump added.

In a letter released Thursday, the President announced the U.S. was calling off talks with Kim Jong-un in response to recent rhetoric by the regime, in which it called Vice President Mike Pence a “political dummy,” and lashed out at John Bolton after the suggested the hermit kingdom use the ‘Libya Model’ as a roadmap for denuclearization.

“Sadly, based on the tremendous anger and open hostility displayed in your most recent statement, I feel it is inappropriate, at this time, to have this long-planned meeting,” Trump wrote.

“You talk about your nuclear capabilities, but ours are so massive and powerful that I pray to God they will never have to be used.”

Read a copy of the full letter below: