US President Donald Trump (L) and North Korean leader Kim Jong-un (Photo: AFP/VNA)

At a Tuesday press conference hosted by the Wall Street Journal, Mr. Bolton added that Washington will attend the summit whenever Pyongyang wants.

US President Trump said the same day that he is expecting optimistic movement from North Korea as he has received a warm letter from North Korean leader Kim.

North Korea suspended the anniversary of the first US-North Korea summit due to unexpected reasons, Straits Times said.