Cheong Wa Dae said it was aware that President Donald Trump had sent a letter to the North's leader Kim Jong-un.
"The government assesses the exchange of personal letters between the leaders of the North and the US positively in terms of maintaining the momentum of their dialogue," Cheong Wa Dae spokesperson Ko Min-jung said in a statement.
She added that South Korea had knowledge of Trump's latest letter to Kim via "communication" with the ally.
Earlier in the day, Pyongyang announced that Kim had received an "excellent" and "interesting" message from Trump.
After reading the letter, the North's leader said "with satisfaction that the letter is of excellent content," according to the Korean Central News Agency.
It went on to say in the English-language report that, "Appreciating the political judging faculty and extraordinary courage of President Trump, Kim Jong-un said that he would seriously contemplate the interesting content."
The state-controlled news agency did not specify when and how the letter was delivered to Kim.
Apparently, it was Trump's reply to a recent letter from Kim.
Making public that he got the letter from Kim a few days ahead of the June 12 anniversary of their landmark Singapore summit, Trump described it as "beautiful" and "very warm."
Despite a stall in denuclearization talks, South Korean President Moon Jae-in repeatedly cited the relatively good relationship between Trump and Kim as a positive signal. (Yonhap)