"Radical" changes in the global economy have left Russia in "dire straits," and it should seize the moment to reform, the country's finance minister has told CNBC.

Speaking on the sidelines of the G-20 summit in Istanbul, Russia's Finance Minister Anton Siluanov said: "We all note that lots of changes are happening, and these change are radical and rapid."

Russia's economy has been hit hard over the last year by the severe decline in global oil prices – down around 50 percent since last June -- and Western sanctions imposed on the country for its part in the Ukraine conflict. This, in turn, has caused the ruble to weaken dramatically and pushed up the rate of inflation to around 15 percent.

The "hardships" facing Russia have slowed down the pace of growth, Siluanov said, but should encourage the Russian authorities to reform.

"In the times when all prices were soaring, when inflow of foreign currency was substantial and when the ruble was strong there was lots of room for complacency," he said. "Now that we've found ourselves in dire straits, we have no choice but to carry on with the reform that has been postponed for so long."