The Russian ruble is tumbling further down, under pressure from low oil prices.

The currency was down nearly 3 percent in morning trading in Moscow on Tuesday, floating around 65 rubles per dollar.

The ruble has been battered by slumping global prices for oil, Russia's main revenue earner, and Western sanctions over Ukraine. Last year, it was the world's worst performing currency along with the Ukrainian hryvnia.

Russia's central bank has tried to shore up the ruble by sharply raising its key interest rate and selling its reserves. The bank's foreign currency reserve has dropped below $400 billion for the first time since August 2009.

Russia's economy is expected to contract by more than 4 percent this year if oil prices remain at their current level.