Standard & Poor's Ratings Services cut its rating on Russia to one notch above junk, citing large capital outflows in the first quarter.

S&P cut its rating one level, to BBB-minus from BBB. It kept its outlook on the country negative, where it has been since March 20, when the ratings firm lowered it from stable in light of heightened tension in Ukraine and the prospect of economic sanctions.

"In our view, the tense geopolitical situation between Russia and Ukraine could see additional significant outflows of both foreign and domestic capital from the Russian economy and hence further undermine already weakening growth prospects," S&P wrote in its report.

Moscow's MICEX stock index fell by 1.5% after the move. The ruble weakened 0.6% against the dollar to 35.977.

A further cut to junk status would be a big move, given Russia's relatively modest level of debt, according to Tim Ash, an economist at Standard Bank.