The West must stand up to Russia over the conflict in Ukraine or Europe could descend into a major war for the first time since 1945, diplomats warned yesterday as efforts to negotiate peace hung by a thread.
A former US ambassador to Ukraine predicted that Estonia and the other Baltic states - all members of Nato - could be Vladimir Putin's next targets if he is allowed to hold on to territory won by force.
Read more: Leaders agree on peace plan for Ukraine
The Estonian President, Toomas Hendrik Ilves, compared Western inaction against Russia with the appeasement of Adolf Hitler under the Munich Agreement of 1938, when Nazi Germany was allowed to seize parts of the former Czechoslovakia.
"We know from history that appeasement will never satisfy those that are being appeased," he said. "Munich 1938, I think, should be a lesson to all of us, even today."
The British Foreign Secretary Philip Hammond accused Mr Putin of "acting like some mid-20th century tyrant", while his French counterpart, Jean-Yves Le Drian, said he would "fear the worst" if peace talks this week failed.
Last night, reports put the death toll from the conflict at 50,000 - 10 times previous estimates.
The US has considered sending weapons to Ukraine, but the UK, Germany and France oppose arming Kiev's forces, saying this could lead to an escalation of the fighting.
Writing in The Independent, the former Liberal Democrat leader, Lord Ashdown, urged the West to use "military diplomacy", while avoiding direct conflict.
"The right reaction to the Russian arming of the Ukrainian rebels is to make it clear Russian arming of the Ukrainian rebels is to make it clear we are prepared to do the same for the Ukrainian government," he writes.
"Start small, slow and unaggressively - with communications and intelligence equipment for example."
But a hardline with the Kremlin over Ukraine should be matched with efforts to build a strategic partnership with Moscow in the fight against Isis and Islamist terrorism, Lord Ashdown added.
The worst-case scenario facing Europe was outlined yesterday by John Herbst, former US ambassador to Ukraine, who said it was time to send military help to Ukraine.
"I think that those who argue against helping Ukraine defend itself against a much bigger and stronger aggressor do not understand the strategic stakes," Mr Herbst said.
"[Putin's] statements, his provocations against the Baltic states, against Kazakhstan, indicate his goals are greater than Ukraine. If we don't stop Mr Putin in Ukraine, we may be dealing with him in Estonia.
"I'm not saying we will, but he has given indication that this could happen. The most important national security challenge in the world today is a rogue Kremlin and we need to stop him and Ukraine is the place to do it."
Mr Ilves told Sky News that while he was not yet afraid of a Russian invasion, action must be taken to halt its "reckless and irresponsible behaviour throughout our region".
The peace summit due to take place in Minsk on Wednesday was described by Mr Hammond as "one of the last opportunities that Russia will have to avoid further significant damage to its economy" if the world is forced to increase its sanctions against the Kremlin.
He said any peace deal would have to include a Russian withdrawal from Crimea, which it annexed from Ukraine following a disputed referendum.
"Don't make it sound like that is an outrageous thing for us to demand," Mr Hammond said.
"This man has sent troops across an international border and occupied another country's territory acting like some mid-20th century tyrant.
"We do not see any reason to tolerate this kind of outrageous and outdated behaviour from the Kremlin."
Push for peace at summit
Mr Putin, Ukrainian President Petro Poroshenko, German Chancellor Angela Merkel and French President Francois Hollande are all due to take part in the Minsk summit.
However, Mr Putin, who has repeatedly talked peace while his forces carry out attacks on the ground, suggested that the negotiations might not actually happen.
"We will be aiming for Wednesday, if by that time we are able to agree on a number of the positions that we recently have been discussing intensely," he said.T
he mixed messages from Moscow continued with Foreign Minister Sergey Lavrov saying Russia expected "important decisions" would be made at the meeting.
Ms Merkel is expected to brief US President Barack Obama on the state of negotiations during a previously scheduled trip to Washington today.
Dismissing talk of a transAtlantic rift, US Secretary of State John Kerry said yesterday that America and its European allies were "united in our diplomacy" on Ukraine.
"There is no division, there is no split," he said.
US Senator John McCain, said "defensive arms" should be sent to the Kiev government as a matter of urgency.
"The Ukrainians are being slaughtered and we're sending them blankets and meals. Blankets don't do well against Russian tanks," he said.
Germany's Frankfurter Allgemeine Sonntagszeitung newspaper reported yesterday that German intelligence estimated up to 50,000 soldiers and civilians had been killed during the conflict, nearly 10 times higher than Kiev's estimate.
"The official figures are clearly too low and not credible," a source said.