WASHINGTON: Top Republicans aligned with U.S. President Donald Trump pushed Ukrainian President Volodymyr Zelenskiy on Sunday to change his position on the war with Russia or step aside, ramping up pressure on the Ukrainian leader after a contentious White House meeting last week.

European leaders gave a show of support to Zelenskiy at a meeting in London on Sunday, with British Prime Minister Keir Starmer urging his counterparts to step up their defense efforts, just two days after Trump and Vice President JD Vance clashed with Zelenskiy in the Oval Office, spurring him to leave early without signing a planned minerals deal.

The blowup, which showcased Vance in an attack dog role for his boss, stunned leaders around the world and raised questions about the next phase of the war, which Russia started by invading Ukraine three years ago, and Trump's efforts to end it.

Zelenskiy argued in the meeting that Russian President Vladimir Putin had not honored a 2019 ceasefire agreement and described him as a killer and a terrorist.

Trump's national security adviser, Mike Waltz, said it was not clear to the administration that Zelenskiy was ready to negotiate an end of the war. Waltz underscored Trump's goal for a permanent peace between Moscow and Kyiv involving territorial concessions in exchange for European-led security guarantees.

Asked whether Trump wanted Zelenskiy to resign, Waltz told CNN's "State of the Union" program: "We need a leader that can deal with us, eventually deal with the Russians and end this war."

"If it becomes apparent that President Zelenskiy's either personal motivations or political motivations are divergent from ending the fighting in his country, then I think we have a real issue on our hands," Waltz added.

U.S. Senator Lindsey Graham of South Carolina, a top Trump ally and also an advocate for Ukraine, questioned whether the United States could still work with Zelenskiy following the White House clash in remarks to reporters on Friday.

House of Representatives Speaker Mike Johnson issued a similar message on Sunday.

"Something has to change. Either he needs to come to his senses and come back to the table in gratitude, or someone else needs to lead the country to do that," the top congressional Republican told NBC's "Meet the Press" program, referring to Zelenskiy.

"I'd like to see Putin defeated, frankly. He is an adversary of the United States. But in this conflict, we've got to bring an end to this war."

'ABSOLUTELY SHAMEFUL'

U.S. Senator Bernie Sanders, an independent from Vermont aligned with the Democrats, dismissed suggestions that Zelenskiy should resign.

"I think that is a horrific suggestion. Zelenskiy is leading a country, trying to defend democracy against an authoritarian dictator, Putin, who invaded his country," Sanders said on "Meet the Press." Republican U.S. Senator James Lankford of Oklahoma said on the same program that he did not agree with calls for Zelenskiy to resign.

Democrats have expressed disgust over the tenor of Trump's meeting with the Ukrainian leader.

U.S. Senator Chris Murphy of Connecticut lambasted the White House for drawing closer to Russia than to fellow democracies.

"It is absolutely shameful what is happening right now. The White House has become an arm of the Kremlin," he said on CNN's "State of the Union" program. "The entire pretext for that meeting... was an attempt to rewrite history in order to sign a deal with Putin that hands Putin Ukraine. That is disastrous for U.S. national security."

Waltz called it "absolutely false" that the Oval Office meeting was an ambush, and the Trump administration put the onus on the Ukrainians to shift their position.

"We'll be ready to reengage when they're ready to make peace," Secretary of State Marco Rubio said on ABC's "This Week" program. He said he had not spoken to Zelenskiy or Ukrainian Foreign Minister Andrii Sybiha since the Friday meeting.

"No one here is claiming Vladimir Putin is going to get the Nobel Peace Prize this year," Rubio said, while arguing that negotiations with Moscow were required. "You’re not going to bring them to the table if you’re calling them names, if you’re being antagonistic."

Democrat Amy Klobuchar, a U.S. senator from Minnesota, said on "This Week" that she was "appalled" by the clash in the Oval Office and that she had met with Zelenskiy before he went to the White House on Friday.

"There is still an opening here" for a peace deal, she said.