President Trump said late Sunday there is a “psychological deadline” for Russia to agree to a ceasefire in Ukraine, shortly after he had expressed frustration with Russian President Vladimir Putin.

“It’s a psychological deadline,” Trump told reporters aboard Air Force One when asked if there was a deadline for Russia to agree to a deal. “If I think they’re tapping us along, I will not be happy about it.”

Trump said he did not think Russia was dragging the U.S. along, saying he believes Putin “wants to make a deal.” He went on to criticize Ukrainian President Volodymyr Zelensky, suggesting he was wavering over a deal to grant the U.S. access to Ukraine’s mineral supply. Multiple outlets reported the Trump administration put forward a new proposal last week.

“And if he does that he’s got some problems. Big, big problems,” Trump said of Zelensky. “We made a deal on rare earth 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.”

Trump told NBC’s Kristen Welker on Sunday he was “very angry, pissed off” at Putin for suggesting there should be new leadership in Ukraine. He also threatened to impose additional sanctions on Russian oil if Moscow did not come to the table to end the fighting in Ukraine.

Russian forces invaded Ukraine in February 2022 after amassing troops near the border. Trump campaigned on a pledge to end the fighting, and his administration has met with officials from both Russia and Ukraine to seek a ceasefire agreement.

Critics have argued Putin is not interested in a lasting peace in Ukraine, with some Democrats suggesting the Trump administration is being strung along while Moscow makes gains on the battlefield.