Donald Trump has paused US military aid to Ukraine just days after his row with President Zelenskyy.
A White House official, speaking anonymously, said: "President [Trump] has been clear that he is focused on peace.
"We need our partners to be committed to that goal as well. We are pausing and reviewing our aid to ensure that it is contributing to a solution."
There was no indication about the possible length of the pause, and there's been no comment so far from Ukraine.
It comes after the astonishing clash between the two leaders - as well as vice president Vance - in the Oval Office on Friday.
Donald Trump's berating of Mr Zelenskyy was condemned by many and has led to a show of support from European leaders as they try to formulate their own way forward.
The US president attacked the Ukrainian leader again on Monday, telling reporters he should be "more appreciative".
Writing on Truth Social, Mr Trump also said Mr Zelenskyy had made "the worst statement that could have been made" after he commented that peace was still "very, very far away".
"America will not put up with it for much longer!" he posted.
"It is what I was saying, this guy doesn't want there to be peace as long as he has America's backing," the president added.
Mr Zelenskyy then posted on X that Ukraine was "working together with America and our European partners and very much hope on US support on the path to peace".
"Peace is needed as soon as possible," he said.
'Music to the ears of Putin'
By David Blevins, US correspondent
President Trump's decision to pause military aid to Ukraine marks a significant shift in US foreign policy, one previously considered unthinkable.
This blow to Ukraine's defences in the face of Russian aggression will be music to the ears of President Putin. US military aid has kept Ukraine in this David and Goliath battle for three years.
It has funded what military analysts simplify as "the big stuff" of battle – artillery, anti-tank weapons, rockets and armoured vehicles. Trump’s decision to push pause disregards efforts by Keir Starmer and other European leaders to devise a peace plan.
Those already questioning Europe's reliance on the US for defence will conclude they have been given the answer.
But the decision sets President Trump up for a potential confrontation with Republicans, who had approved the funding, in Congress.
White House sources say he wants President Zelenskyy to go on TV and apologise for the jaw-dropping showdown last Friday. But the Ukrainian president feels he has no apology to make for expressing his doubt about Russia's commitment to peace.
Earlier, Trump side-stepped a question about a Kremlin diplomat claiming the US administration and Moscow were now aligned on foreign policy.
This weakening of Ukraine's defence capability moves that question front and centre as he prepares to address Congress on Tuesday.
Despite the diplomatic crisis, President Trump has said a deal is still possible.
An agreement giving the US access to Ukraine's rare earth metals was meant to have been signed by the two presidents on Friday.
It was billed as an important step in a future peace deal - and part payback for aid already received.
However, the dramatic falling out has thrown that into jeopardy.
Mr Zelenskyy wants the metals deal to include guarantees on halting Russia should it break the terms of any peace agreement.
Zelenskyy showed 'lack of respect'
Vice president JD Vance suggested on Monday that the metals pact was the best way to secure a lasting end to the war.
"If you want real security guarantees, if you want to actually ensure that Vladimir Putin does not invade Ukraine again, the very best security guarantee is to give Americans economic upside in the future of Ukraine," Mr Vance told Fox News.
"That is a way better security guarantee than 20,000 troops from some random country that hasn't fought a war in 30 or 40 years," he added.
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Mr Vance said President Zelenskyy had shown a "lack of respect" and "a certain sense of entitlement" in Friday's trip to Washington.
He repeated that the door was still open if he altered his approach, but told Fox News he "still isn't there".
European and world leaders - who met President Zelenskyy at the weekend - have discussed a potential "coalition of the willing" to deploy peacekeepers and deter further Russian aggression.
The prime minister said Britain was prepared to put "boots on the ground and planes in the air" under the plan - but it's unclear who else might participate.
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Read more:
Long-range drones 'weakening Russia's combat ability'
Zelenskyy: 'I am exchangeable for NATO membership'
The coalition that could secure peace in Ukraine
Keir Starmer told MPs on Monday that Britain must "lead from the front" on supporting Ukraine and the "security of our continent, the security of our country".
However, the prime minister believes any international deployment of troops must have a US "backstop" deterrent to be taken seriously by Russia.
America has given around €64bn of military aid to Ukraine, compared with €62bn from European nations (including Britain).
The overall US total is €114bn and the European one €132bn. This includes humanitarian aid and other financial assistance to keep the country running.
Following the weekend summit, the UK also pledged £1.6bn in finance for Ukraine to buy another 5,000 air defence missiles.