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.

Trump will host South Korean President Moon Jae-in at a summit at the White House on May 22, and the two are expected to discuss the upcoming summit between Trump and North Korean leader Kim Jong Un.

The Blue House intends to "sufficiently convey (to the United States) what we've discerned about North Korea's position and attitude through the summit on the 22nd, and sufficiently convey the United States' position to North Korea," thereby helping to bridge the gap between their positions, the official said.

"Seeing the announced statements and responses from North Korea and the United States, we see the two parties as having a sincere and serious attitude (to stand in each other's shoes)," the official said.

South Korea intends to continue discussions with North Korea to hold high-level talks North Korea cancelled on Wednesday, Blue House said in a statement on Thursday. North Korea called off the talks, blaming U.S.-South Korean military exercises.

Meanwhile, Chinese government's top diplomat, Wang Yi, said on Thursday the measures North Korea has taken to ease tension on the Korean peninsula should be acknowledged, and all other parties, especially the United States, should cherish the opportunity for peace.