Talks between the United States and North Korea are headed in the right direction, a top U.S. envoy said on Friday, ahead of a rare visit to the White House by a senior North Korean official.

At a planned meeting with U.S. President Donald Trump in Washington, Kim Yong Chol, a close aide of Kim Jong Un, will hand over a letter from the North Korean leader as the two sides try to put a derailed summit meeting back on track.

Trump hopes to meet Kim Jong Un in Singapore on June 12 and pressure him to give up his nuclear weapons, although he conceded on Thursday that might require more rounds of direct negotiations.

“I’d like to see it done in one meeting,” Trump told Reuters. “But often times that’s not the way deals work. There’s a very good chance that it won’t be done in one meeting or two meetings or three meetings. But it’ll get done at some point.”

In Seoul, U.S. negotiators expressed optimism after meeting their North Korean counterparts for preparatory talks at Panmunjom, on the fortified border between the two Koreas.