Western sanctions on Russia could last for decades, according to the country's economy minister Alexei Ulyukayev.

The United States and the European Union slapped Russia with economic penalties after it annexed Crimea from Ukraine in March, sparking a conflict in eastern Ukraine between pro-Russian separatists and Ukrainian government forces.

The minister said the sanctions on Russia would probably last "for a very long time" and were not easily reversible.

"When a US law is passed it is very hard to change it afterwards – looks like it will be in place for decades," said Ulyukayev, as cited by Russia's Vedomosti newspaper.

The US and EU have accused Russia of fuelling the fighting in eastern Ukraine by supplying arms and manpower to rebel groups, imposing sanctions against individuals with close ties to Putin as well as on companies and specific sectors of the economy including the defence and financial sectors.

2015 recession

Russia's economy is widely expected to plunge in to a recession in 2015, with a series of factors dragging it in to the red.

Ulyuakayev described the scenario as a "perfect storm," adding that a lack of structural reform had left it vulnerable to external factors.

A major oil and gas exporter, Russia has suffered as the crude oil price fell drastically in the second half the year. Oil and gas make up around two thirds of Russia's total exports of around $530bn. The Kremlin relies on revenues from the state-owned oil and gas firms to fund around half of its annual budget. With oil prices falling by almost half since June, the government can expect its revenues to slide accordingly.

Meanwhile, the Russian ruble has plunged in line with the falling oil price. In a dramatic week of trading, the ruble reached a low of 80 against the dollar on Tuesday but rebounded on Wednesday. It was trading at 61 against the dollar by early afternoon Thursday in London.

The sanctions would have a greater impact in 2015, Ulyukayev said, as the oil markets could slide further.

"The situation is so hard to predict that we cannot be prepared for its changes in the future...Write one more stress scenario in addition to $60 [a barrel]? Let's do it for $40, $20 ad $10," he said, as cited by Vedomosti.