Russia's central bank is running down its stash of foreign cash to try to stop its currency from plunging and contain the crisis threatening its economy.

So far this year the central bank has burned through more than $110 billion in foreign currency supplies. That's more than a quarter of what it has in reserves right now.

Russia's total international reserves, which also include gold and other liquid foreign assets, had fallen to $398.9 billion by December 19.

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Spending has ramped up in the last few weeks. Since the start of December, the central bank has blown through more than $21 billion.

That, along with a series of other measures to support the banking sector, has helped to stabilize the ruble.

Russia is working on a plan to pump one trillion rubles ($18.6 billion) into Russian banks next year, and wants to establish deposit insurance to guarantee savings up to 1.4 million rubles ($26,000).

The ruble climbed nearly 6% against the U.S. dollar on Friday.

Still, Sberbank CIB chief economist Evgeny Gavrilenkov said the central bank's strategy of spending down foreign reserves was "not ideal," and pointed to stresses elsewhere in the financial sector.

"The liabilities of banks and servicing [refinancing] debt is very costly now, so the banking system is vulnerable," he said.

Last week a local bank collapsed, and the rates Russia banks lend to each other have jumped. Overnight rates are now nearly 19%, indicating just how serious the funding crisis has become.

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Despite the recent bounce in the ruble, the Russian economy remains under heavy clouds. With more than half the government's revenue drawn from oil and gas exports, prolonged weakness in oil prices will savage growth. This week the country had its debt placed under review for a potential downgrade to junk status.

And that means no holiday cheer for government officials, as President Vladimir Putin ordered all members of parliament to work through the Christmas and New Year period as they fight to keep the battered economy together.