President Donald Trump said Sunday that Ukrainian President Volodymyr Zelenskyy is trying to back out of a rare earth deal with the U.S., adding if he does that he is going to have "some problems."

"I think Zelenskyy, 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 said while speaking to reporters on Air Force One on Sunday. "We made a deal on rare earths, and now he’s saying, ‘well, you know, I want to renegotiate the deal.’ 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."

Zelenskyy said last month that Ukraine is ready to sign an agreement on minerals and security with the U.S. at any time, noting that the agreement is seen as a step toward greater security and solid security guarantees.

Zelenskyy’s statement came after a visit to the White House where the two leaders were expected to sign an agreement on rare Earth minerals. But the visit turned sour, and Zelenskyy was kicked out of the president’s home with no deal in hand.

While speaking to reporters on Sunday, Trump said he and his team were making progress on a ceasefire deal between Ukraine and Russia.

Trump explained that Putin had said some things over the last few days about Zelenskyy not being credible, adding he was not happy about that. But, Trump added, he thinks Putin is going to be good. He also said he would not want to put secondary tariffs on Russia.