After nearly a year of violence in Ukraine, European leaders on Thursday backed a peace agreement in a last-ditch attempt to quell escalating fighting. Amid doubts about the deal’s chances for success, the biggest winner appeared to be Russian President Vladimir Putin, who neatly short-circuited Western discussions about imposing new economic and military costs for his role in fueling the war.

After marathon negotiations, Ukrainian and pro-Russian rebel leaders agreed to a cease-fire beginning at the start of Sunday, and Ukraine accepted sweeping measures to grant rebel-held territories more self-rule. But the leaders of Ukraine, Germany and France cautioned that the deal was fragile, and it was unclear why this one would succeed when a similar bargain in September quickly fell apart.

So it was left to Putin to claim victory in the efforts to end a fight in which he has always denied taking part.

Ukraine committed itself to politically tricky efforts to grant rebel-held territory new freedoms. Leaders from the European Union agreed to sit down with the Kremlin to discuss Russian concerns about Ukraine’s efforts to align itself with them. Putin offered little — but he eliminated, at least for now, the possibility of stronger E.U. sanctions and of U.S. weaponry for Kiev’s military.

Leaders emerged after 15 hours of talks that began Wednesday evening and stretched without interruption until noon Thursday.

French President François Hollande, left, Ukrainian President Petro Poroshenko and German Chancellor Angela Merkel. (Mykola Lazarenko/AFP/Getty Images)

“This was not the best night of my life, but the morning, in my opinion, was good,” Putin said in the marble-clad Palace of Independence in the Belarusan capital of Minsk. “We still managed to agree on the essentials.”

Leaders, diplomats and fighters on the ground all agreed Thursday that the cease-fire set to begin Sunday would face great challenges. There were few mechanisms to ensure that heavy weaponry would be rolled back
at least 30 miles from the front lines, nor was there agreement about the status of the crucial Ukrainian-held railroad hub of Debaltseve, where as many as 8,000 Ukrainian soldiers may be surrounded by rebels.

And a key Ukrainian demand to regain full control of its border with Russia was put off until the end of the year. Rebels have seized hundreds of miles of frontier, creating an open path for weapons and fighters to flow from Russia.

At least 5,400 people have been killed in the 10-month-old conflict, according to U.N. estimates, and more than a million people have been displaced from their homes. The conflict has raised tensions between Russia and the West to Cold War-era levels. Russia’s March annexation of Ukraine’s Crimean Peninsula is a separate flash point that did not enter into this week’s discussions.

Stone-faced Ukrainian leaders focused on what they had gained, not what they had given up.

“It was not easy. In fact, various unacceptable conditions, including retreat and surrender, were made,” said Ukraine’s Western-backed president, Petro Poro­shenko. “But we did not bow to any ultimatums.”

In a measure of the leaders’ lack of confidence in the deal, they signed no binding documents, leaving that to lower-level Ukrainian, Russian and rebel leaders. Instead, the quartet of leaders agreed to a nonbinding statement in which they confirmed the “full respect of the sovereignty and territorial integrity of Ukraine.”

“We now have a glimmer of hope,” German Chancellor Angela Merkel said. But she also noted that “there are still major hurdles that lie ahead.”

But the deal was enough to halt talk in both Washington and Brussels of further sanctions. There was scant mention of sending U.S. arms to the Ukrainian military, a specter that last week was enough to send the German and French leaders speeding to Moscow to seek peace with Putin.

“The United States is prepared to consider rolling back sanctions on Russia when the Minsk agreements of September 2014, and now this agreement, are fully implemented,” Secretary of State John F. Kerry said in a statement.

There was similar no-more-sanctions talk in Brussels, where E.U. leaders met to discuss the deal.

“Today, the issue is not going to be discussion about further sanctions, as some were already decided in the past days, but rather the positive ways in which the European Union can contribute” to furthering peace, E.U. foreign policy chief Federica Mogherini said.

The Russian economy has suffered because of international sanctions and the recent sharp fall in the price of oil, but Putin remains immensely popular at home. European leaders have said that they believe he is willing to escalate militarily in Ukraine far beyond the support that the West could offer Kiev.

Still, top officials said Thursday that if this deal falls apart, different approaches would be needed.

“If it fails, there is going to be a change of strategy, not only by the United States but also by some of the European countries,” said Latvian Foreign Minister Edgars Rinkevics.

One prominent American voice in favor of arming Ukraine said Thursday’s outcome was only to be expected.

Putin has “great cards, and he’s playing them well,” said Ivo H. Daalder, a former U.S. ambassador to NATO. “He doesn’t let anyone know what his bottom line is.”

Daalder added: “We’re constantly telling him what our bottom line is, and that’s that . . . we don’t want a military confrontation, period.”

After the painful negotiations — in which it appeared briefly that Ukrainian officials and rebels would walk out in frustration — the sides agreed to a 13-point deal whose core was similar to a September agreement that was never fully complied with and collapsed in recent weeks. Rebels won concessions on territory and autonomy, a measure of Putin’s hard-nosed bargaining.

In addition to the cease-fire and military pullback, the two sides agreed to start negotiations about local elections. Kiev committed to pardoning rebels for their participation in the fighting, and it agreed to end an economic blockade of the east.

Poroshenko also promised to pass a new constitution by the end of the year that would decentralize power. That step would require wide backing in the Ukrainian parliament, and it was unclear that he had the political muscle to do it, given the unpopularity of the measure.

Separately on Thursday, Ukraine reached a preliminary accord to expand an International Monetary Fund-led bailout to $40 billion to avert a default. The separatist conflict has battered the Ukrainian economy and drained the country’s resources, and the government is close to default.

In eastern Ukraine, neither the military nor pro-Russian separatists reported any reduction in violence Thursday. Both sides reported casualties from overnight shelling, and intense fighting was reported near Debaltseve and the port city of Mariupol, which rebels have long coveted.

Several analysts said that even if fighting died down, violence was likely to resume before any of the more wide-ranging measures could be implemented, as happened after the September agreement.

Putin “is in favor of peace as long as it allows him to reach his goals, and then he switches to war,” said Alexander Golts, a
Moscow-based military analyst and journalist. “This isn’t the last cease-fire in this conflict.”

Karoun Demirjian and Natasha Abbakumova in Moscow and Carol Morello and William Branigin in Washington contributed to this report.