Russia has strongly criticised the visit to Washington by Ukraine’s Volodymyr Zelensky, accusing the US of fighting an indirect war against it.
President Joe Biden has pledged $1.85bn (£1.45bn) of military aid for Ukraine – including an advanced missile system to help guard against Russian attacks.
In a defiant address to US lawmakers, Mr Zelensky welcomed the assistance.
But Russia’s US ambassador said these “provocative actions” would lead to an escalation with severe consequences.
Anatoly Antonov told Russian state media that Moscow was “trying to appeal to common sense at all levels”, but talk of delivering the Patriot missile system to Kyiv was “deeply disturbing”.
Patriot missiles are capable, effective and expensive. The White House says they will help defend Ukrainians against “Russia’s barbaric attacks on Ukraine’s critical infrastructure”.
Moscow has complained that no calls for peace were heard during President Zelensky’s trip to Washington – with spokesman Dmitry Peskov describing this as proof that the US was fighting a proxy war with Russia.
Mr Peskov added that delivering Patriot missiles would not prevent Russia from “achieving its goals during the special military operation”.
“The talks in Washington have shown that neither Ukraine nor the United States is seeking peace. They are simply intent on continuing the fighting,” said Russian foreign ministry spokesperson Maria Zakharova.
Russian commentators have echoed this – repeatedly accusing the US of “pumping Ukraine full of weapons”.
Some media reports from Moscow ridiculed the Ukrainian leader – with state TV’s Channel One comparing him to a stripper begging for money. On Wednesday, he was likened to a toilet brush.
Marking his first foreign trip since the start of the invasion, Mr Zelensky told Congress his country was “alive and kicking” and would never surrender to Moscow.
As well as the $1.85bn package that has already been announced, another $45bn of US emergency assistance is currently before the Senate.
Mr Zelensky expressed hope this extra funding would be approved, to “help us to defend our values and independence”.
But there are signs that US support is likely to face greater political scrutiny. Republican support for continued assistance has been eroding.
In a survey conducted in November, just over half of Republican voters supported aid to Ukraine – down from 80% in March.
The party, which will take control of the House of Representatives in January, has warned it will not write a “blank cheque” for Ukraine.
But President Biden has vowed to stick by Ukraine “for as long as it takes”.
At a joint news conference, Mr Biden told reporters he was “not at all worried” about holding the international coalition together.
Despite concerns some allies may be feeling the strain of the conflict’s cost and disruption to global food and energy supplies, the US president said he felt “very good” about the solidarity of support for Ukraine.
As Ukraine’s most important ally, the US has already committed $50bn (£41bn) of humanitarian, financial and security assistance – far more than any other country.
On his way home from Washington, Volodymyr Zelensky stopped in Poland where he met Polish President Andrzej Duda, one of his strongest allies.
The two discussed the US visit as well as their “strategic plans for the future”, Mr Zelensky said.
Since Russia invaded Ukraine on 24 February, the US military estimates that at least 100,000 Russian and 100,000 Ukrainian soldiers have been killed or injured, along with some 40,000 civilian deaths.
The UN has recorded 7.8 million people as refugees from Ukraine across Europe, including Russia. However, the figure does not include those who have been forced to flee their homes but remain in Ukraine.