Angela Merkel says a peace plan is worth trying, as Emily Buchanan reports
A peace plan drawn up by France and Germany is "one of the last chances" to end the conflict in east Ukraine, French leader Francois Hollande says.
German Chancellor Angela Merkel said it was unclear if the plan would succeed, but it was "definitely worth trying".
Mr Hollande said the plan would include a demilitarised zone of 50-70km (31-44 miles) around the current front line.
The leaders are attempting to end the fighting in Ukraine between government troops and pro-Russia rebels.
Russia is accused of arming pro-Russian separatists in eastern Ukraine - claims it denies.
Mr Hollande, Mrs Merkel and Russian President Vladimir Putin have agreed to develop a peace plan together, which they will discuss with Ukraine's leader Petro Poroshenko by telephone on Sunday.
Few details of the plan have emerged, but it is thought to be an attempt to revive a September ceasefire, signed in Minsk in Belarus. Since then the rebels have seized more ground, raising alarm in Kiev and among Ukraine's backers.
The UN says fighting has left nearly 5,400 people dead since April, when the rebels seized a big swathe of the Luhansk and Donetsk regions following Russia's annexation of Crimea.
Intense fighting in the strategic town of Debaltseve has forced many to flee their homes
The US is considering providing the Ukrainian forces with defensive weapons
Mr Hollande and Mrs Merkel visited Kiev and Moscow earlier this week, in what appeared to be a speedily arranged visit to discuss the peace proposal.
Diplomatic talks are continuing Saturday at an international security conference in the German city of Munich.
Speaking there, Russian Foreign Minister Sergey Lavrov said he "sincerely" hoped the latest peace plan would "produce results".
Meanwhile, Mr Hollande warned reporters that the consequences of continued fighting were serious. "If we fail to find a lasting peace agreement, we know the scenario perfectly well... it is called war."
He also told French TV that eastern Ukrainian regions would need extensive autonomy. "These people have gone to war," he said. "It will be difficult to make them share a common life."
Mrs Merkel told the conference that while there was no guarantee that the latest push for a diplomatic resolution would succeed, it was essential to try to reach a peace deal. "I believe we owe that much to those who are affected in Ukraine," she said.
Rebels say they have captured the town of Vuhlehirsk in Donetsk
Asked about signals that the US is considering pleas to send weapons to Ukraine to fend off the rebels, she said: "There is already a large number of weapons in the region and I don't see that this has made a military solution more likely."
The statement put her in opposition to Nato's top military commander, US Air Force general Philip Breedlove, who told reporters that Western allies should not "preclude out of hand the possibility of the military option".
Analysis: Jonathan Marcus, BBC News, Munich
The German Chancellor - speaking here in Munich for the first time since her return from her peace mission to Kiev and Moscow - has provided a fascinating insight into her own political underpinnings.
She passionately defended her opposition to the idea of selling arms to Ukraine - something that is under active consideration in Washington.
She pointed to her own personal experience - she said that as a girl she had seen the Berlin Wall go up but nobody had intervened to help the citizens of what became the Eastern bloc, because there was no realistic expectation of success. Her implication was that this realism was needed now.
Her view is that no amount of weaponry will convince Mr Putin that Russia would lose militarily. More arms she insisted would lead to more victims.
There was significant applause at these remarks, though noticeably neither US Vice-President Joe Biden or the Ukrainian President Petro Poroshenko were clapping.
Questions any peace plan would have to address include the route of any new ceasefire line - given the rebel advances of recent weeks - how to enforce it, and the future status of the conflict zone, says the BBC's Sarah Rainsford in Moscow.
Moscow is still denying any direct role in the conflict, while Kiev insists above all that Ukraine must remain united, our correspondent says.
Meanwhile, the Secretary General of Nato, Jens Stoltenberg, told the BBC that he had seen evidence of increased support for the rebels from Moscow.
What is Russia's army buying? - in 90 seconds
"We have seen an increase in the supply of heavy equipment - artillery, tanks, advanced air defence systems. And some of these equipments [sic] are very advanced, they can only come from Russia."
Some 1.2 million Ukrainians have fled their homes since the Ukraine conflict began.
"The situation is getting very dire indeed," Michael Bociurkiw, a spokesman for the Organisation for Security and Co-operation in Europe (OSCE) special monitoring mission in Ukraine, told the BBC.
"Over the past few days over 3,000 people have been evacuated," he said, adding that overcrowding in some evacuation centres meant that evacuees were being temporarily accommodated in train carriages in cold conditions.
