The outlook for Russia's recession-hit economy remains weak, as it struggles with international sanctions and weak oil prices,  ratings agency Standard & Poor's said Friday.

S&P said it expected the Russian economy to expand by about 0.4 percent annually between 2015 and 2018, well down on the average 2.4 percent seen in the previous four years.

S&P kept its "BB+/B' long- and short-term foreign currency rating for Russia.

"The ratings remain constrained by our view of Russia's relatively weak political institutions and economic income and growth prospects, which we believe impede the economy's competitiveness and business and investment climate," the S&P statement said.

The report comes after the World Bank downgraded the outlook for Russia late last month, warning the economy would likely shrink by 3.8 percent in 2015 and plunge more Russians into poverty.

S&P said Russia's prospects were hampered by weak political governance and the continuing crisis in Ukraine.

The predicted weak growth "also reflects a lack of external financing due to the introduction of economic sanctions and the sharp decline in oil prices," S&P said.

Russia slipped into recession at the start of this year as oil prices plunged and Western sanctions, imposed over Moscow's role in the Ukraine conflict, began to bite.

Against this backdrop, the ruble fell 20 percent against the dollar, reaching its lowest level this year in August and pushing up consumer prices.

The collapse of the currency will hit per-capita GDP in dollar terms, S&P said, forecasting it would be $8,700 in 2015, down from $14,500 in 2013.