Paris (AFP) - US billionaire investor George Soros warned Thursday that Europe's very existence was being threatened by Russia, in a scathing criticism of the EU's response to the Ukraine crisis.

The 84-year-old, in an article published in Le Monde daily and the New York Review of Books, said European reluctance to provide military and financial assistance to Ukraine could be its downfall and urged member states to make an immediate $20 billion (16 billion euros) cash injection to the struggling country.

"It is high time for the members of the European Union to wake up and behave as countries indirectly at war," said the financial wizard whose often spot-on predictions on crises are carefully scrutinised.

"All available resources ought to be put to work in the war effort even if that involves running up budget deficits. Not only the survival of the new Ukraine but the future of NATO and the European Union itself is at risk.

"In the absence of unified resistance it is unrealistic to expect that (Russian leader Vladimir) Putin will stop pushing beyond Ukraine when the division of Europe and its domination by Russia is in sight."

- Europe has 'lost its way' -

Soros argued that as a result of the 2008 financial crisis, the European Union and eurozone had lost their way.

With austere fiscal rules sparking popular resentment and a surge in anti-Europe parties, Russia was presenting an alternative "in some ways superior to the European Union -- more flexible and constantly springing surprises."

Soros said Putin had taken advantage of the reluctance of Europe and the United States to take any firm action as it annexed Crimea and set up separatist enclaves in eastern Ukraine, where regular Russian forces have been fighting the Ukrainian army.

He slammed both the unwillingness to provide military support as well as the withholding of financial support until after a key parliamentary vote on Sunday.

"This has led to an avoidable pressure on Ukrainian currency reserves and raised the spectre of a full-blown financial crisis in the country."

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Soros said Putin was likely to use a gas deal with Kiev to try and get Ukrainian President Petro Poroshenko to appoint a prime minister palatable to him after Sunday's vote, a deal the leader was unlikely to accept.

Further afield, Soros said he suspected that Putin "may be holding out the prospect of a grand bargain in which Russia would help the United States against ISIS", referring to Islamic State jihadists who have seized swaths of Iraq and Syria.

"What is worse, President Obama may accept such a deal. That would be a tragic mistake, with far-reaching geopolitical consequences."

Soros warned that preserving Ukraine was more important than fighting IS, as the collapse of Ukraine would see a victorious Russia posing a far wider threat and the EU become "even more divided and ungovernable."