The Russian currency was being traded at about 31.4 against the dollar after starting the month at the 29.0 mark. A similar decline against the euro to around 43.0 saw the ruble slip into a trading range last seen in the closing stages of the global financial crisis.

Alfa Bank said the slide has caused Russia's central bank to intervene in currency trading for the first time this month after initial indications that it was happy with the currency decline.

A weaker ruble helps Russia's exporters but risks fanning inflation because of the rising price of imports.

Alfa Bank said a part of the ruble's decline may be linked to companies' plans to pay off $50 billion in foreign currency debts by the end of the year.

But other analysts pointed to foreign investor decisions to close their positions in Russia and other energy-producing markets whose growth is tied closely to the price of oil.

"Increasingly intense global headwinds ... and a faltering investor appetite for risk are pushing down high-beta currencies, of which the ruble is a prominent representative, as positions are liquidated," Renaissance Capital said in a research note.

Copyright AFP (Agence France-Presse), 2011