Los Angeles, March 31 -- US President Donald Trump said Sunday that Ukrainian President Volodymyr Zelensky is attempting to back out of a rare earth minerals deal with the United States, warning that if he does that, he could have "problems."

"I think Zelensky, by the way, he's trying to back out of the rare earth deal, and if he does that, he's got some problems -- big, big problems," Trump told reporters on Air Force One.

Trump said that a deal had already been made regarding rare earth minerals, but now, Zelensky is looking to renegotiate. "He wants to be a member of NATO. Well, he was never going to be a member of NATO. He understands that, so, if he's looking to renegotiate the deal, he's got big problems," said Trump.

On March 20, ...