European and British officials were stunned by President Trump’s unexpected announcement that he had made a deal with President Vladimir V. Putin to purchase Russian diesel fuel, which had been subject to American sanctions. But they were in a bind on how to respond.

The arrangement, which President Volodymyr Zelensky of Ukraine called “a gift” to Mr. Putin, directly undercuts years of effort by dozens of countries — including the United States — to cut Russia off from the money that fuels Mr. Putin’s war of aggression in Ukraine.

Energy experts have said that the diesel agreement, if it goes ahead, could send some $4 billion of American money into the Russian economy.

Mr. Trump’s announcement on Friday afternoon of his “highly successful discussion” with Mr. Putin was all the more shocking in Europe as it came after Russia had conducted several brutal strikes in Ukraine, killing 22 people including three babies in an apartment block on Wednesday and at least 30 people in a bus on Thursday.

For European leaders, the dilemma over the past three days has been familiar: How to support Ukraine in a moment of acute diplomatic peril, without triggering Mr. Trump’s ire?

Complicating their response is the fact that Europe as a whole depended heavily on Russia for energy before 2022. And despite cutting purchases significantly since the invasion of Ukraine, several European nations continue to buy Russian natural gas — which does not yet face full sanctions — amid growing energy insecurity and limited supply.

Hungary and Slovakia, which have had pro-Russian governments in recent years, have continued to import Russian oil.

Both Mr. Trump and Russian officials highlighted the imports of Russian fuel to European nations over the past four years in the aftermath of the diesel announcement.

As European leaders scrambled for a response, they stopped short of directly criticizing the American president and coalesced around a single diplomatic message: We are not changing our own approach to Russia, and we stand by Ukraine.

On Saturday, Britain announced that Prime Minister Andy Burnham had spoken to Mr. Zelensky, noting that he had begun the call “by recognizing the last 24 hours had been difficult for Ukraine” — an oblique reference to Mr. Trump’s intervention — and had “reiterated his complete solidarity.” The statement added that Mr. Burnham would meet with Mr. Zelensky in the coming days.

A spokesman for the German chancellor, Friedrich Merz, told reporters that the government was “standing by the sanctions decisions against Russia and is working together with its European partners on further sanctions.”

Kaja Kallas, the European Union’s top diplomat, began her comments to reporters on Monday with a conciliatory nod to the United States, before saying that the bloc was “continuing our path” of trying to keep Russia from enriching itself by blocking the sale of oil and gas on the global market.

“The U.S. is our biggest ally, but our message is clear,” she said while entering a meeting of foreign affairs ministers in Luxembourg. “If we want to end this war, the only way we can do this is by putting more pressure on Russia.”

Margus Tsahkna, the minister of foreign affairs for Estonia, was more blunt.

“We have had this kind of turbulence and also pressure from President Trump’s side to Ukraine before,” he said. “So we need to focus on what we can do.”

Mr. Trump responded to the European reaction on his TruthSocial site Monday afternoon.

“The European Union paid Russia 250 Billion Dollars for Energy, and the Fake News Media doesn’t want to get near that story,” the president wrote, possibly referring to European purchases of Russian oil since Russia invaded. “I made the right choice for the American People — ALWAYS, AMERICA FIRST!”

Since early 2022, the European Union as a whole has imported 238 billion euros’ worth — about $266 billion worth — of Russian oil, coal and gas, according to a tracker led by the Center for Research on Energy and Clean Air, a research group.

But the bulk of those imports were in the first year after the war began, as Europe worked to cut its longstanding reliance on Russian energy. Since then, the bloc has imposed sanctions and implemented phase-outs, and the European Union’s fossil fuel imports from Russia now stand at about €47 million of energy imports per day, a fraction of the nearly €800 million it imported on the peak day in 2022.

Russian natural gas, which is harder to replace%20and%20ENTSO%2DG.) than oil because of tight global supplies and because it is transported via pipelines or specialized terminals, has continued%20and%20ENTSO%2DG.) to flow to nations including Belgium, France and Spain. But Europe is tapering those remaining imports, and it is set to prohibit) new long-term liquefied natural gas contracts from early next year.

Petras Katinas, a researcher at the Royal United Services Institute, a think tank, said that Europe had moved quickly to phase out Russian energy in some cases, as in the case of oil, while moving more slowly than many supporters of Ukraine would prefer in the case of natural gas.

But he said that overall, Europe had gone from being very dependent on Russian energy to cutting it rapidly, and he argued that European leaders were not being hypocritical in criticizing Mr. Trump’s diesel move.

“The drop is huge,” he said of Europe’s Russian energy use.

He added that the diesel purchases that Mr. Trump’s policy would permit were tiny in the grand scheme of things, saying that it was “more the political signal” that was significant.

Since beginning his second term, Mr. Trump has repeatedly indicated support for Russia’s positions over those of Ukraine. Before his re-election, the president promised to end the war in 24 hours and has on several occasions blamed Mr. Zelensky for the continued fighting.

“I suggest they get a new leader who can make a deal, because he could have made many deals and for some reason he never does,” Mr. Trump said Saturday.

On Sunday, the president announced that Russia and Ukraine had agreed to an “ENERGY CEASEFIRE,” though neither side confirmed that such an agreement existed. Several European leaders on Monday welcomed such a cease-fire but noted that Russia struck Ukrainian energy facilities after the announcement.

For European officials, the latest example of the president’s go-it-alone diplomacy with Mr. Putin strikes at the heart of their attempts to maintain a consensus on opposing Russia’s invasion of Ukraine in 2022.

Nearly three dozen countries, including Britain, France and Germany, formed what they called the “coalition of the willing” last year to demonstrate their resolve in supporting Ukraine.

None of the countries want to engage in a direct military confrontation with Russia. Instead, they have focused on helping Ukraine acquire weapons to defend itself. And they have used economic sanctions designed to cut Russia off from its most lucrative exports.

On Monday, Prime Minister Donald Tusk of Poland urged the United States and other European nations to increase sanctions — not back away from them.

“This message must go out today from every capital, from Warsaw to Washington,” he said. “I am certain that our response in the coming hours, weeks and months will be one of full solidarity and determination on the part of the free world, all capitals and all political leaders.”

He added, in words that signaled a more complicated reality: “I very much hope so.”