South Korea is seeking to mediate to bridge the gap between the United States and North Korea as they appear to have "some kind of difference in stances" ahead of a planned summit, an official at South Korea's presidential Blue House said on Thursday.

The comments come after Pyongyang on Wednesday threatened to pull out of the June 12 summit in Singapore with U.S. President Donald Trump, saying it might not attend if Washington continues to demand it unilaterally abandon its nuclear arsenal.

The Blue House official said the South Korean government or President Moon Jae-in intends to more actively perform "the role of a mediator" in various channels between South Korea, the U.S. and North Korea.