Vladimir Putin is expected to give his response on Sunday to the Franco-German plan for a Ukrainian ceasefire, enforced with the creation of a demilitarised zone along the frontlines.

The plan, according to the French president, François Hollande, proposes a buffer zone of 50km to 70km and requires Russian-backed separatists to withdraw to ceasefire lines that were agreed in Minsk in September. In return, the eastern provinces would be given greater autonomy.

Angela Merkel, who travelled with Hollande to Moscow on Friday evening to set out their proposal, was downbeat about its prospects on Saturday. The German chancellor told the annual Munich Security Conference: “It is uncertain whether it will lead to success but, from my point of view and that of the French president, it is definitely worth trying.”

She conceded that it was “disappointing” that Russia had failed to abide by the Minsk agreement. On Russian guarantees, she admitted “the experience has not been good” but added: “The answer to this can’t be not to enter any agreements at all. Of course we have to try again and again.”

Also speaking at Munich, Russian foreign minister Sergey Lavrov said he hoped the latest diplomatic drive would “produce results, and those results will be supported by the parties to this conflict”.

Hollande and Merkel are expected to speak by video link on Sunday to Putin as well as to Ukrainian president Petro Poroshenko in what Hollande portrayed as a last-ditch bid to contain the conflict, in which 5,300 people have so far died. “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,” he told reporters in the city of Tulle in central France.

In a highly charged appeal to an audience of senior European and American officials in Munich, Poroshenko said: “We need simple things. We need a ceasefire. Can you imagine that anyone in the 21st century can be against a ceasefire? We should have an answer in just a few hours and, if not, then days.”

The conference revealed the deep and widening divide between the west and Russia, with the audience openly laughing at claims by Lavrov and other Russian officials that Moscow had no troops in the Ukrainian conflict.

However, the conference also highlighted an emerging rift on how to respond if the peace initiative fails and fighting escalates. It pits eastern European nations and increasingly vocal members of the US Congress, who want to send arms to the Ukrainian government, against western European states who are against such a move. In the middle is the Obama administration, which says it has not made up its mind.

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Speaking in Munich, vice-president Joe Biden maintained the ambiguity of the White House position. “We will continue to provide security assistance to Ukraine,” he said. “We believe in an honourable peace. We also believe that Ukrainians have the right to defend themselves.”

The US has previously agreed to provide non-lethal military assistance to Ukraine, but according to its own accounting, reported by the Bloomberg news agency, only half of the $118m of American equipment has so far been delivered. Among the items not yet delivered are armoured trucks and other vehicles, medical supplies, binoculars, sleeping bags and tents.

In his Munich speech, Poroshenko derided Russian denials of military involvement in his country, brandishing the passports and identity cards that he said belonged to Russian soldiers killed or captured while fighting in Ukraine. He suggested sarcastically that they had “lost their way” in military vehicles with full fuel tanks.

The Ukrainian president issued a passionate appeal for arms. “People will either support a sovereign and independent Ukraine, or Russia wins. This conflict must be resolved, not frozen,” he said. “We are an independent nation and we have a right to defend our people … Our lack of defensive capability triggers offensive attacks and brings escalation.”

He suggested equipment Ukraine needs did not have to be lethal, saying that anti-artillery radar, communications and jamming technology would improve defences.

Despite repeated challenges from eastern European leaders, and Bob Corker, chairman of the Senate foreign relations committee, Merkel remained opposed to supplying more arms to Ukraine. “I am firmly convinced that the conflict cannot be resolved by military means,” she said. “The progress that Ukraine needs cannot be achieved with more weapons. There are already a lot of weapons there … I cannot envisage any situation in which improvement in the equipment of the Ukrainian army so impresses Putin that he concedes militarily. You have to look reality in the eye.”

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The British foreign secretary, Philip Hammond, said Britain shared the German position. “We are not for the current time considering the supply of lethal equipment to the Ukrainians,” he told journalists, adding that the policy could change if there was a radical change of the situation. He noted that the American voices calling for arming Kiev were so far mostly from Congress and that “no decision has been taken by the US administration”.

“There can’t be a military solution to this problem. It has to be a political solution. As long as there is something approaching a military stalemate, the focus must be on finding a political solution.” He said European sanctions were already a powerful coercive tool to persuade Putin to make peace. Hammond acknowledged that the election of a pro-Russian government in Athens would make it harder to get EU consensus to renew sanctions, but he said the Greek government would ultimately have to make a deal with the troika of the EU, the International Monetary Fund and the European Central Bank.

“Of course the Greeks will want to use their bargaining power to get the best deal they can but they will also be aware you can flex a line but if you break it, that will have negative consequences for you.”

Hammond said that the Franco-German peace proposal recognised that the frontline in Ukraine has shifted since the Minsk agreement in favour of the separatists. But he insisted it did not concede those gains, but laid down means to roll back the lines to where they were. “We have to start with the reality that the line of contact is now in a different place from where it was last November,” he said. “That does not mean accepting that line of contact, but it does mean the disengagement plan has to start from the recognition of the reality of where the line of contact is now.”