US President Donald Trump has said next week's summit with Kim Jong-un is a "one-time shot" at peace.
A meeting between Mr Trump and the North Korean leader Mr Kim will take place on Tuesday in Singapore.
Mr Trump described the summit as a "mission of peace", but said that the two leaders were in "unknown territory in the truest sense".
Mr Trump comes to Singapore after falling out with other world leaders over tariffs at a G7 summit in Canada.
En route, he tweeted an upbeat message about the forthcoming summit with Mr Kim.