WASHINGTON—The White House said it is working to arrange a second meeting between President Trump and North Korean leader Kim Jong Un, signaling an attempt to revive the stalled diplomatic efforts between Washington and Pyongyang.

White House press secretary Sarah Sanders confirmed that Mr. Kim had sent a letter requesting to meet with Mr. Trump.

She said the letter was “very warm” and “very positive” and said the administration was “open to and already in the process” of arranging a second meeting.

Ms. Sanders said the White House wouldn’t release the letter unless North Korea agrees to do so, but described it as a “further evidence of progress” in the relationship between the two leaders.

The two leaders met for the first time in June in Singapore, which Messrs. Trump and Kim declared to be a successful start in de-escalating tensions and opening further talks on North Korean denuclearization.