WASHINGTON (Reuters) - White House national security adviser Mike Waltz said on Friday he expects Ukrainian President Volodymyr Zelenskiy to sign a minerals agreement with the United States as part of efforts to end the Ukraine war, while President Donald Trump said Kyiv has no cards to play with.

Zelenskiy's office said the Ukrainian president's chief of staff, Andriy Yermak, discussed "aligning positions" in bilateral relations in a call with Waltz on Friday after sharp exchanges between Trump and the Ukrainian leader.

Trump denounced Zelenskiy as a "dictator" on Wednesday and warned he had to move quickly to secure peace with Russia or risk losing his country, deepening a feud between the two leaders.

The sharp change in tone from the United States, Ukraine's most important backer, has alarmed European officials and stoked fears that Kyiv could be forced into a peace deal that favors Russian President Vladimir Putin.

Zelenskiy had said Trump was trapped in a "disinformation bubble", but later toned down his statements and said he was hoping for American pragmatism.

Zelenskiy on Wednesday rejected U.S. demands for $500 billion in mineral wealth from Ukraine to repay Washington for wartime aid, saying the United States had supplied nowhere near that sum so far and offered no specific security guarantees in the agreement.

In the call with Waltz, Yermak "stressed the importance of maintaining bilateral cooperation and a high level of relations between Ukraine and the United States," Zelenskiy's office said.

A few hours later Waltz told the Conservative Political Action Conference on the outskirts of Washington: "Here's the bottom line, President Zelenskiy is going to sign that deal, and you will see that in the very short term."

Waltz said on Thursday Zelenskiy needed to come back to the negotiating table.

Asked about Waltz's latest comments, a Ukrainian government source said the two sides were "still in talks".

'THEY DON'T HAVE ANY CARDS'

Speaking at a White House event on Friday, Trump was critical of Zelenskiy while holding off on negative comments about Putin.

"I've had very good talks with Putin, and I've had not such good talks with Ukraine," Trump said. "They don't have any cards, but they're playing tough."

The German government said on Friday German Chancellor Olaf Scholz and Zelenskiy had spoken by phone and agreed that Ukraine must have a seat at the table in future peace talks.

Polish President Andrzej Duda urged Zelenskiy on Friday to keep up calm and constructive cooperation with Trump, following the U.S. president's criticism of him.

"I suggested to President Zelenskiy to remain committed to the course of calm and constructive cooperation with Donald Trump," Duda wrote on the X social media platform.

"I have no doubt that President Trump is guided by a deep sense of responsibility for global stability and peace."

Duda, whose term in office expires in 2025, was one of Trump's preferred international partners during his 2017-2021 presidency and they have described themselves as friends.

Poland's president is due to meet Trump in Washington on Saturday, Poland's state news agency PAP reported.

Zelenskiy said on Friday he had discussed in a call with Duda the dialogue with the U.S. team led by Ukraine envoy Keith Kellogg.

"It is important that the United States stand with us. A strong and lasting peace can only be achieved through unity," Zelenskiy said on X.

(Reporting by Steve Holland, Nandita Bose, Trevor Hunnicutt and David Brunnstrom in Washington and Tom Balmforth in London; Editing by Ros Russell)