President Volodymyr Zelensky of Ukraine called on world leaders not to abandon his country, citing the recent death of a Russian dissident as a reminder that President Vladimir V. Putin of Russia would continue to test the international order, and pushing back against the idea of a negotiated resolution to the war.
Mr. Zelensky, speaking on Saturday at the Munich Security Conference, said that if Ukraine lost the war to Russia, it would be “catastrophic” not only for Kyiv, but for other nations as well.
“Please do not ask Ukraine when the war will end,” he said. “Ask yourself why is Putin still able to continue it.”
The two topics that have loomed over nearly every discussion at the yearly meeting of world leaders have been Russia and the potential weakening of trans-Atlantic relations, amid an increasingly pessimistic assessment of Kyiv’s ability to beat Moscow.
Mr. Zelensky’s speech on Saturday came as Ukrainian forces retreated from a longtime stronghold, Avdiivka, giving Russian troops their first significant victory in almost a year.
And it came a day after attendees of the conference were shaken by the news that the prominent dissident Aleksei A. Navalny had died in a Russian Arctic penal colony. It was a stark reminder, Mr. Zelensky warned, of how Moscow would continue to test the Western-backed international rules-based order.
“This is Russia’s war against any rules at all,” Mr. Zelensky said. “But how long will the world let Russia be like this? This is the main question today.”
Mr. Zelensky’s impassioned call was in dramatic contrast to his last appearance in Munich, two years ago. At that moment, an invasion seemed inevitable, but European officials were still insisting, despite the satellite evidence of massing troops, that Mr. Putin was bluffing. Even Mr. Zelensky, in his public appearance on the same stage that he used on Saturday, had said he did not believe Mr. Putin would dare to attack.
This year, Mr. Zelensky’s message was that the death of Mr. Navalny on Friday, and the evidence of Russian military buildups, should also make Europeans believe that Mr. Putin would not stop at Ukraine’s borders.
In conversations with reporters at the conference, European and American officials said that they saw no evidence, for now, that Mr. Putin wants to bring NATO forces into the war. But European leaders have started to warn repeatedly in recent weeks that a victory for Mr. Putin could embolden him to test NATO’s resolve, particularly if the American commitment to the alliance wavers.
The mood among many at the conference was deeply pessimistic, with European leaders consumed by discussions over how to ensure their own security after the U.S. presidential election in November that could see another term for former President Donald J. Trump, who last week invited Russian aggression against NATO members who did not pay their fair share.
And European officials repeatedly pressed their American counterparts about Washington’s inability so far to pass a $60 billion U.S. aid package for Ukraine, which passed the Senate but may yet be scuppered by Republicans in the House.
“People are looking at us with disbelieving eyes,” one leader of the American delegation here, who would not speak on the record, said on Saturday morning. “We’ve been talking about leading this fight, and we’ve spent the past two days telling the Europeans to come up with a Plan B to arm Ukraine.”
Included in those discussions is the possibility of having Germany, among others, buy American arms and deliver them to the Ukrainian front if Congress does not find the money. But at the same time, military officials are talking about new technologies with the Ukrainians, including the possibility of helping with new generations of drones that could fly in swarms at Russian emplacements.
Debate has also been swirling in recent weeks over whether European nations should arrange for their own nuclear deterrence beyond that provided by Washington and NATO.
NATO’s secretary general, Jens Stoltenberg, said in his own comments on Saturday that such talk was “not helpful.” Any questioning of NATO’s nuclear umbrella, he argued, “would only undermine NATO in a time when we really need credible deterrence.”
Vice President Kamala Harris said after meeting Mr. Zelensky on Saturday that support from her and President Biden was “unyielding and unending.”
Mr. Zelensky, in return, urged her to bring about American consensus on support for Ukraine. “We need now your unity,” he said.
In his speech, Mr. Zelensky argued it was a “myth” that Ukraine could not win. “We can get our land back and Putin can lose.”
But he stressed, as the House goes on a two-week recess without approving the Ukraine aid, that there was no time to waste: “Remember, everyone, that dictators do not go on vacation.”