It will be "very hard" to maintain economic growth in Russia amid sanctions pressure on its energy sector, the head of Russia's largest bank said Friday.

Last week, the European Union enforced a new round of sanctions targeting Russian energy efforts in shale, arctic oil and deep waters. The U.S. and European governments already have imposed punitive sanctions on Russian energy companies Rosneft, Gazprom Neft and others in response to the crisis in Ukraine.

Herman Gref, the director of Russian bank Sberbank, told Rossiya-24 television the sanctions, which extend into the banking realm, were taking their toll.

Russian Prime Minister Dmitry Medvedev said earlier this month the government had a responsibility to support companies like Rosneft, controlled in part by the Kremlin.

The European Bank for Reconstruction and Development said sanctions "have negatively affected business confidence in Russia."