"A letter to President Trump from Chairman Kim was received on August 1. The ongoing correspondence between the two leaders is aimed at following up on their meeting in Singapore and advancing the commitments made in the US-DPRK joint statement," Sanders said.
Trump responded to Kim's letter and the White House will deliver his letter shortly, Sanders said.
As Sarah Huckabee Sanders noted, the US was open to discussions of setting up a second meeting between US President Donald Trump and North Korean leader Kim Jong-un.
"There is not a second meeting that is currently locked in or finalized. We're certainly open to that discussion, but there isn't a meeting planned," Sanders said when asked if plans exist for a second meeting between Trump and Kim following their first summit meeting in Singapore on June 12.
The first letter was received by US President Donald Trump in July: with it, the North Korean leader predicted that "epochal progress" in promoting bilateral ties would "bring our next meeting forward."
On Wednesday, Trump thanked Kim in a Twitter message for sending back to the United States the remains of US soldiers killed in the 1950-1953 Korean War. Trump also said he is looking forward to meeting Kim again soon.
The historical and long-anticipated meeting between the two leaders took place in Singapore on June 12. They signed a joint declaration pledging to rid the Korean peninsula of nuclear weapons and recover Korean War dead.