US President Donald Trump and South Korea's Moon Jae-in are due to hold talks in Washington, amid uncertainty over a planned US-North Korea summit.
Last week the North said it may cancel the summit if the US insists on it giving up nuclear weapons unilaterally, reports BBC.
Mr Moon will try to calm US nerves to get talks back on track, observers say.
One of his officials said he would "likely tell President Trump what to expect and what not to expect from Kim", Yonhap news agency reported.
The historic 12 June summit is due to take place in Singapore.