MINSK, Belarus -- A cease-fire and an overall compact to end the war in eastern Ukraine were announced here Thursday by the leaders of France, Germany, Russia and Ukraine after marathon overnight bargaining that threatened to derail the attempt. Even as the agreement was announced, it appeared fragile, with officials on all sides saying there was more work to be done.
The cease-fire is scheduled to take effect at midnight Saturday, but fact that the leaders used three separate news conferences to announce the accord suggested a lack of unity. Still, after such a concentrated effort, all the leaders chose to accent the idea that there was at least a chance that the yearlong war could be quieted.
The negotiations "consisted of a long night and a long morning, but we have arrived at an accord on a cease-fire and a global end to the conflict," President François Hollande of France said. "It is a relief for Europe."
Hollande said a broader agreement on ending the war would hinge on border control and the resolution of questions like the withdrawal of heavy weapons.
The talks appeared to be in doubt Thursday as the four leaders negotiating the agreement canceled news briefings intended to announce an accord and returned to the negotiating table.
President Vladimir Putin of Russia, President Petro Poroshenko of Ukraine and Hollande, along with German Chancellor Angela Merkel, haggled for more than 15 hours in talks that had begun Wednesday evening.
In the morning, rather than presenting the results at a collective briefing, the Russian and Ukrainian presidents had each planned to address reporters from their countries, while the leaders of Germany and France met with a different set of journalists. Officials had said hours earlier that there would be a joint briefing in the press room of the ornate Independence Palace, where the negotiations have taken place.
Ukrainian Foreign Minister Pavlo A. Klimkin sent out a tweet not long after dawn, saying that members of some delegations were "literally sleeping" but that the negotiators for Kiev were still going strong.
Part of the urgency was that Merkel and Hollande were due at a Thursday afternoon summit meeting of the European Union in Brussels, which Poroshenko was also scheduled to address. Having committed themselves to making one last effort to secure peace, however, it seemed that the French and German leaders were determined to wrest an agreement from the talks before leaving.
The return to the negotiating table was accompanied by a flurry of Russian news agency reports that Poroshenko had declined at the last minute to accept the outlines of the deal that addressed the independent status of the breakaway areas of Donetsk and Luhansk, as well as the demarcation line meant to form the spine of a demilitarized zone.
The separatists and their Russian patrons want a federal system that gives the breakaway regions control over their foreign and economic policies, while Poroshenko had vowed that only some manner of decentralization was acceptable.
In addition, the truce line has shifted since an original deal was signed in September, creating a more cohesive whole from the two breakaway regions. The town of Debaltseve remains a point of contention, with the Ukrainian troops holding it now surrounded.
As the peace talks stalled, fighting continued in the disputed areas of southeastern Ukraine.
Pro-Russian rebel forces mounted a counterattack on areas east of the coastal city of Mariupol, trying to retake some of the ground seized in recent days by the volunteer, right-wing Azov Battalion.
Residents of the industrial port on the Sea of Azov, widely expected to be the next target of rebel attacks if the Minsk peace talks did not produce a truce, could hear heavy shelling throughout the morning.
City and military officials said the fighting was confined to small villages to the east.
Rick Lyman contributed reporting from Kharkiv, Ukraine.