The ruble, Russia's currency, has suffered its biggest one-day fall since 1998 as sinking oil prices and Western sanctions over the Ukraine crisis aggravate worries about the country’s economy.

The Russian currency fell by nearly nine percent at one point to 53.9 rubles against the dollar and 67 rubles against the euro. Later in the day, the currency clawed back a little ground to 52 rubles against the dollar and 65 against the euro.

The ruble has depreciated by nearly 60 percent against the dollar since the start of this year.

The price of oil dropping to five-year lows in recent days has a major impact on the Russian economy as oil and natural gas exports are a main source of revenue for its federal budget.

Many analysts increasingly worry over the country's economic outlook as the Russian authorities express apparent reluctance to change tack over the crisis in Ukraine.

The price of oil, the backbone of the Russian economy, has dropped roughly 25 percent since the summer. Brent crude, an international benchmark, fell three percent on Friday and was down another one percent on Monday to $69.47 a barrel.

The US and the EU imposed economic sanctions on Russia over the summer, targeting the country’s energy, banking and defence sectors to punish, what they say, Moscow's support for rebels in eastern Ukraine.

The Kremlin, which in the past supported the exchange rate by buying up the rubles, said it considered the recent pressure on the currency to be speculative and was happy for it to remain freely floated in markets.

Meanwhile, some Russian politicians asked prosecutors to probe the central bank over its decision to let the ruble float freely.