File photo of Angela Merkel. (Associated Press)

Germany's Angela Merkel today ruled out sending weapons to the Ukrainian government to fight pro-Russian separatists but said there was no guarantee that her latest peace initiative with French President Francois Hollande would work either.

Speaking at a Munich conference today attended by top US, European, Ukrainian and Russian officials, Ms Merkel said the Franco-German peace plan presented to Kiev and Moscow this week was worth trying, but "it is uncertain if it will succeed".

Mr Hollande cast it as a last-ditch effort to end fighting in eastern Ukraine that has killed more than 5,000 people. With Russia's earlier annexation of Ukraine's Crimea peninsula, the crisis has driven Moscow's relations with the West to new lows.

"If we don't manage to find not just a compromise but a lasting peace agreement, we know perfectly well what the scenario will be. It has a name, it's called war," Mr Hollande told reporters in the city of Tulle in central France.

Debate at the high-profile Munich Security Conference focused on an emerging rift between America and Europe on over how to confront Putin as the Moscow-backed rebels gain territory. US President Barack Obama is under pressure from some in Congress to provide Kiev with lethal weapons.

NATO's top military commander, US Air Force general Philip Breedlove, gave the strongest signals yet in Munich that he now wants the Western allies to consider sending weapons to Ukraine.

"I don't think we should preclude out of hand the possibility of the military option," General Breedlove told reporters, adding that he was referring to weapons or capabilities and that there was "no conversation about boots on the ground".

In Kiev today, the Ukrainian military spokesman said separatists had stepped up shelling of government forces on all front lines and appeared to be massing for new offensives on the key railway town of Debaltseve and the coastal city of Mariupol.

Ms Merkel and Mr Hollande flew home from Moscow in the dead of night after five hours of talks with Mr Putin on Friday that yielded little beyond a promise to keep talking.

Ms Merkel, who in Munich held three-way talks with Ukrainian President Petro Poroshenko and US Vice-President Joe Biden and will fly to Washington tomorrow to meet Mr Obama, questioned the logic of sending arms to fight separatists who are believed to have unlimited supplies of weapons from their Russian backers.

"I understand the debate but I believe that more weapons will not lead to the progress Ukraine needs. I really doubt that," the conservative German leader 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."

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