The value of the Russian ruble hit a historic low Monday when compared with U.S. and European currencies, the Russian Central Bank said.

It took just over 40 rubles to buy one U.S. dollar, or just over 50 rubles to buy a euro, in Monday trading, the bank said.

The bank said last week it was struggling to keep Russian inflation in check because of U.S. and European sanctions on Russian energy companies. Sanctions were imposed earlier this year because of Russian policies in eastern Ukraine, where pro-Kremlin rebels are fighting for more authority.

Exports of crude oil, petroleum products and natural gas account for nearly 70 of all Russian export revenues in 2013. The World Bank finds Russia's export-based economy leaves it vulnerable to geopolitical tensions.

Victoria Nuland, U.S. assistant secretary of state for the Bureau of European and Eurasian Affairs, said last week sanctions "can and will" be rolled back provided Russia respects Ukraine's sovereignty.

Nuland left Sunday for Kiev to discuss the status of the conflict in eastern Ukraine.