North Korea's reclusive leader Kim Jong-un has asked South Korean President Moon Jae-in to visit Pyongyang at the "earliest date" possible for what will be a third inter-Korean summit, Kim's sister told the South Korean leader.

The invitation was delivered in a meeting between Moon and the North Korean leader's sister, Yo-jong.

Kim Yo-jong was earlier considered part of a high-level North Korean delegation to the PyeongChang Winter Olympic Games, but Cheong Wa Dae spokesman Kim Eui-kyeom said she was here as a special envoy of the North Korean leader.

"While delivering a letter from Kim Jong-un, chairman of the State Affairs Commission, which contained his stated willingness to improve South-North Korea relations, special envoy Kim Yo-jong orally delivered Chairman Kim Jong-un's invitation (for Moon) to visit the North at a time convenient to him, saying he is willing to meet President Moon Jae-in at the earliest date possible," the spokeswoman told a press briefing.