President Trump has tweeted that a deal with North Korea is “very much in the making”, a day after revealing he had agreed to meet its leader Kim Jong-un.
North Korea has yet to make a statement.
Earlier, the White House said the meeting would not take place unless Pyongyang takes “concrete actions” first.
US media report that Mr Trump made the decision to meet without consulting key figures in his administration.
The top US diplomat, Secretary of State Rex Tillerson, was on his first official trip to Africa when the announcement was made.
Speaking to reporters on Friday from Djibouti, Mr Tillerson said: “That is a decision the president took himself.”
“I spoke to him very early this morning about that decision and we had a very good conversation.”
The deal with North Korea is very much in the making and will be, if completed, a very good one for the World. Time and place to be determined.
— Donald J. Trump (@realDonaldTrump) March 10, 2018