US President Donald Trump told a meeting of world leaders Thursday that Europe must stop purchasing Russian oil and put economic pressure on China to try to bring about an end to the war in Ukraine, a White House official told CNN, as the administration seemed to put the onus on its allies to get more involved in stopping the conflict.

Trump made the comments in a Thursday call with Ukrainian President Volodymyr Zelensky and other European leaders in a meeting of the “Coalition of the Willing,” a group of Ukrainian allies trying to end the war and provide security for Ukraine from future attacks.

Following the call, French President Emmanuel Macron said that 26 countries have promised to contribute to a potential peacekeeping force if a ceasefire deal is finalized – though US support for security guarantees is seen as central to lending the Europeans’ actions credibility.

Macron acknowledged as much on Thursday, saying that alongside strengthening Ukraine’s armed forces and deploying European troops to Ukraine, the third component of Ukraine’s security guarantees ought to be an “American safety net.”

“In the coming days we will finalize the American support for these security guarantees,” the French president said.

The developments reflect the intractability of the conflict in Ukraine and the increasing pressure Trump is under to punish Russia as he struggles to push forward negotiations to end the war. Now almost three weeks after his high-stakes Alaskan summit with Russian President Vladimir Putin, Trump is growing increasingly frustrated with the lack of progress on peace and is contemplating how involved he should be personally in brokering a meeting between Kremlin and Ukrainian leaders, administration officials have told CNN.

The White House official said Macron and European leaders called Trump into the coalition meeting, and Trump “emphasized that Europe must stop purchasing Russian oil that is funding the war — as Russia received €1.1 billion in fuel sales from the EU in one year.”

“The President also emphasized that European leaders must place economic pressure on China for funding Russia’s war efforts,” the official said.

The official did not describe any discussion over what security guarantees the president is willing to provide Kyiv should a deal with Moscow be struck.

Trump pledged last month to participate in post-war security guarantees for Ukraine after hosting Zelensky and seven European leaders at the White House, though top Trump administration officials, like Secretary of State Marco Rubio, have argued that Europe should take the lead.

The US has indicated to allies it is open to playing a limited role in providing security guarantees to Ukraine if a peace deal is reached with Russia. Such guarantees could involve US pilots flying manned air support missions, though Trump has ruled out boots on the ground, CNN previously reported.

On Thursday, Zelensky said the strengthening of Ukraine’s air defenses is under discussion, adding that officials also talked about a “new format.”

“We shared it with the partners today and President Trump,” Zelensky said.

Trump also has previously threatened “severe consequences” on Putin if he does not end the war, though the US president is privately wary that doing so could upend talks, Trump administration officials say.

In the meantime, he’s looked to target countries that purchase Russian goods and oil as a way to force Putin’s hand. Asked Wednesday about whether he is considering slapping sanctions on countries that do business with Russia, Trump argued he’s already done so.

“I’ve already done that with regard to India,” Trump said, referencing his decision to raise tariffs on India to 50% for importing Russian oil and helping Russia finance the war.

For his part, Zelensky on Thursday also stressed the importance of ratcheting up pressure Moscow and “all countries who trade with Russia.”

“The Russian economy is pressured and all the countries who trade with Russia are pressured, and we will continue with this,” Zelensky said, adding that “secondary sanctions and special trade tariffs” can help.

Zelensky rejected Putin’s suggestion earlier this week that he’s ready for the two of them to meet in Moscow.

“Our American partners told me that Putin had invited me to Moscow. In my opinion, if someone wants the meeting to not take place, they should invite me to Moscow,” he said.

CNN’s Kaitlan Collins, Victoria Butenko, Svitlana Vlasova, Christian Edwards, Ed Upright and Sophie Tanno contributed to this report.