Washington DC - US President Donald Trump resumed his attempts Monday to blame Ukrainian leader Volodymyr Zelensky for Russia's invasion, falsely accusing him of responsibility for "millions" of deaths.

Trump – who had a blazing public fight in the Oval Office with Zelensky six weeks ago – said that the Ukrainian shared the blame with Russian President Vladimir Putin, who ordered the February 2022 invasion, and then-US president Joe Biden.

The Republican told reporters that there were "millions of people dead because of three people."

"Let's say Putin number one, but let's say Biden, who had no idea what the hell he was doing, number two, and Zelensky," Trump said during a meeting with the visiting president of El Salvador.

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Trump then doubled down on his attack on Zelensky.

"He's always looking to purchase missiles," he said dismissively of the Ukrainian leader's attempts to maintain his country's defense against the Russian invasion.

"When you start a war, you got to know that you can win the war," Trump said. "You don't start a war against somebody that's 20 times your size, and then hope that people give you some missiles."

Relations between Trump and Zelensky have been tense ever since the US president stunned the world by opening talks with Russia in February.

In the run-up to their televised spat on February 28 Trump repeatedly echoed Moscow's talking points – blaming Ukraine for the war and calling Zelensky a "dictator without elections."

Zelensky has since tried to patch things up, including sending a delegation to Washington last week to discuss a mineral deal Trump has called for, that would give the US preferential access to Ukrainian natural resources.

But the US leader has stepped up his rhetoric in the last few days.

Trump however insisted a deal to end the Ukraine war was possible, despite Ukrainian accusations that Moscow is stalling.

"I want to stop the killing, and I think we're doing well in that regard. I think you'll have some very good proposals very soon," Trump said.

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Trump's comments came despite a deadly Russian strike on the Ukrainian city of Sumy on Sunday that killed at least 35 people, one of the deadliest attacks of the war.

The US president said on Sunday that the attack was a "mistake" but did not elaborate.

Russia insisted Monday that its missiles hit a meeting of Ukrainian army commanders.

Zelensky urged US counterpart Donald Trump in a CBS interview broadcast Sunday to visit his country to better understand the devastation wrought by Russia's invasion.