Donald Trump also called the leader of Japan on Monday ahead of his summit with North Korean leader Kim Jong-un. 
That's according to Secretary of State Mike Pompeo, who briefed reporters in Singapore. He says Mr Trump spoke by phone with the Japanese and South Korean leaders as preparatory talks continue between American and North Korean officials ahead of the leader sit-down Tuesday morning.
Mr Pompeo says there is "enormous potential" for the summit, but lowered expectations that the denuclearization of the Korean peninsula will happen after one meeting. He says: "We are hopeful the summit will have set the conditions for future productive talks."
Mr Pompeo also says Tuesday's meeting presents a test of Mr Kim's willingness to agree to deal his nuclear weapons away for "protections" from the United States.