South Korea's presidential office said on Sunday that it expects the exchange of letters between the leaders of North Korea and the U.S. to aid dialogue progress between the two nations.

Presidential spokesperson Ko Min-jung said in a statement that the government positively assesses the exchange of correspondence between U.S. President Donald Trump and North Korean leader Kim Jong-un.

Ko added that the top office was aware of the letter Trump had sent to Pyongyang shortly after receiving one from Kim, and that it will help in terms of maintaining momentum for future dialogue.

Earlier on Sunday, North Korea's state media reported that Kim had received an "excellent" message from Trump, an apparent follow-up to a letter dispatched from the North Korean leader to Trump earlier this month.

The contents of the letters are not known, and it is unclear how the letters were delivered.