Moon Chung-in, a special presidential advisor to South Korean President Moon Jae-in, talks to participants of a forum at Chosun Hotel in Seoul's Jung-gu District, Wednesday. Yonhap

North Korean leader Kim Jong-un's letter sent to U.S. President Donald Trump this week could open up "new possibilities" in relations between the two countries, a special advisor to President Moon Jae-in said Wednesday.

Moon Chung-in, a special presidential advisor and Yonsei University professor, made the remarks after Trump said Tuesday that Kim sent him a "beautiful" and "very warm" letter, the first known correspondence since their no-deal summit in Hanoi in February.

"I don't know the content of the letter, but I think that new possibilities between the North and the United States could open up considering that there had not been any dialogue or contact (between them since the Hanoi summit)," Moon said during a forum on the South Korea-U.S. alliance.

"That (letter) is considerably heartening. ... There have been difficulties after the Hanoi setback, but I forecast that there may be (talks) between the South and the U.S., between the South and the North, and between the North and the U.S.," he added.