The leaders of Germany and France are expected to take peace proposals to Moscow on Friday in a dramatic initiative to end a conflict in Ukraine that has killed more than 5,000 people.
The coordinated trip by Chancellor Angela Merkel and President Francois Hollande to see Russia's Vladimir Putin followed five hours of late-night talks with Ukrainian leader Petro Poroshenko in snow-bound Kiev.
Asked by reporters in Paris on Friday how the talks went, Hollande said: "It's the first step." Merkel, back in Berlin, said it was unclear whether the meeting in Moscow would secure a cease-fire and whether there would be further talks.
Their initiative follows fierce fighting and territorial gains in eastern Ukraine by Russian-backed separatists since a peace blueprint was agreed in Belarus in September.
The growing military pressure has shaken the Ukrainian economy and driven a debate over the possibility of the United States providing Kiev's hard-pressed army with arms.
For Moscow's part, Russia's ambassador to France Alexander Orlov told Europe 1 radio there was an urgent need to avoid war. "I wouldn't say it's a last-chance meeting, but it's not far off," he said.
A collapse in Ukraine's hryvnia currency further highlighted the importance of reaching a deal. It lost nearly a third of its value on Thursday after the central bank halted daily auctions at which it sold hard currency to banks.
Speaking after meeting Poroshenko in Kiev on Thursday, Secretary of State John Kerry said Washington supported diplomacy, but would "not close our eyes" to Russian tanks and troops crossing the border.
President Barack Obama will decide soon whether to provide Ukraine with lethal weapons to fight the separatists, Kerry said.