The United States will abandon efforts to end the war in Ukraine if it proves impossible to broker meaningful progress in the next several days, Secretary of State Marco Rubio said in remarks that piled pressure on Kyiv as he departed Paris on Friday.

“If it is not possible to end the war in Ukraine, we need to move on,” Mr. Rubio told reporters a day after meeting with President Emmanuel Macron of France, adding that the Trump administration would decide “in a matter of days whether or not this is doable in the next few weeks.”

It was not entirely clear from Mr. Rubio’s remarks whether he meant that the United States would merely abandon its effort to reach a 30-day cease-fire between Russia and Ukraine, President Trump’s immediate focus, or abandon Washington’s commitments to Ukraine altogether.

But his remarks were certain to worry Ukraine, which is heavily dependent on American military support, and appeared intended to inject urgency into European efforts to prod Volodymyr Zelensky, the Ukrainian president, toward painful compromise. Mr. Trump has put virtually no pressure on Russia to end the war and at one point claimed that Ukraine was responsible for the Russian invasion in 2022.

While the United States is Russia’s chief interlocutor in the negotiations, Europe has far greater sway over Mr. Zelensky. Mr. Trump said on Thursday that he was “not a big fan” of the Ukrainian leader. By contrast, speaking of his relations with President Vladimir V. Putin of Russia during his first term, Mr. Trump said that “I was the apple of his eye.” It is clear, not least in Kyiv, where Mr. Trump’s sympathies lie.

As Mr. Rubio warned of American impatience, Vice President JD Vance sounded a different note on a visit to Rome with his family. Speaking before a meeting with Giorgia Meloni, the right-wing prime minister who is a favorite of the Trump administration for her conservative views, he said he was “optimistic” about the negotiations to end the fighting in Ukraine.

Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.

Thank you for your patience while we verify access.

Already a subscriber? Log in.

Want all of The Times? Subscribe.