President Donald Trump said Monday that Ukraine's leader Volodymyr Zelensky should be "more appreciative" of US support against Russia's invasion, after they fell out in public.

"Well, I just think he should be more appreciative, because this country has stuck with them through thick and thin," Trump told reporters at the White House.

Asked if a minerals deal between Washington and Kyiv -- which was supposed to be a step towards helping end the conflict was dead -- Trump said: "No, I don't think so."

Trump was asked to confirm reports that he was considering ending military aid to Ukraine but said: "I haven't even talked about that right now.

"I mean, right now, we'll see what happens. A lot of things are happening right now as we speak," he said.

"I mean literally as we speak. I could give you an answer and go back to my office -- the beautiful Oval Office -- I could go back into the Oval Office and find out that the answer is obsolete."

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