Russia has scrambled to halt a run on the rouble, selling billions of reserves to prop up the currency in the worst economic crisis of President Vladimir Putin's 15 years in power.

At the same time, the United States prepared to pile further sanctions on Russia over its actions in Ukraine, which have combined with falling oil prices to produce the perfect storm causing the currency to go into freefall.

The rouble, which lost a fifth of its value in a single day on Tuesday, has lost 60 per cent of its value since the beginning of the year.

After opening down around 3 per cent on Wednesday, it rallied slightly, trading at 66.05 to the US dollar, from 67.88 on Tuesday evening, and at 82.20 to the euro from 85.15.

"This is a very dangerous situation. It could be just days before a full-on run on the banks by account holders," wrote Vedomosti business daily in an editorial on Wednesday, warning of a "panic" mood.

Making matters worse, late Tuesday the White House confirmed that President Barack Obama will sign into law a bill to tighten sanctions against Russia over its role in Ukraine.

Prime Minister Dmitry Medvedev voiced confidence that Moscow can contain the crisis.
"The country has the currency resources to achieve ... all the economic and production goals that you have set," he told a televised emergency meeting of ministers and industry leaders.

The prime minister acknowledged that the rouble had plunged below the "comfort" level for the economy and the public alike.

He said the central bank and the government had worked out a package of measures to stabilise the situation.

The central bank said Wednesday it had spent $US1.96 billion on Monday in a bid to prop up the currency. The regulator has spent more than $US10 billion out of its currency reserves since the start of the month. The currency reserves were worth $US415 billion on December 5.

The central bank late Monday announced a massive hike of its key interest rate to 17 per cent from 10.5 per cent, but the move failed to stabilise the rouble.

Russia's finance ministry on Wednesday said it was also starting to sell its foreign currency to support the rouble.

"The finance ministry considers the rouble extremely undervalued and is starting to sell its leftover currency on the market," spokeswoman Svetlana Nikitina told AFP.

The finance ministry said it has around $US7 billion at its disposal to prop up the rouble.
"We'll do it for as long as it is needed," deputy finance minister Alexei Moiseyev was quoted as saying by Interfax news agency.

President Vladimir Putin has said nothing about the economic crisis this week, his spokesman saying only that this was a matter for the government, not the Kremlin.