White House Press Secretary Sarah Sanders also announced that President Donald Trump will host a meeting with Japan's Prime Minister Shinzo Abe June 7, a week before the Singapore summit.

"Since the president's May 24th letter to North Korean leader Kim Jong Un, the North Koreans have been engaging," Sanders said.

"The United States continues to actively prepare for President Trump's expected summit with leader Kim in Singapore," she said.

The Trump-Kim summit is set for June 12, back on schedule after the US president briefly pulled out, with officials now scrambling to get ready.

Kim Yong Chol, the North Korean leader's right hand man, was expected to arrive Wednesday in New York where he will meet later this week with Pompeo, Sanders said.

"President Trump will meet with Prime Minister Shinzo Abe of Japan on June 7th here at the White House," she said.