Russia's largest and state-run lender Sberbank and the country's No. 1 private lender Alfa Bank said on Wednesday that the new sanctions imposed by the United States would not have a significant impact on the banks' operations.

The U.S. announced a fresh round of sanctions targeting Russian financial institutions, as well as Kremlin officials and their family members, in response to what Russia calls a "special military operation" in Ukraine.

The new sanctions hit Sberbank, which holds one-third of Russia's total banking assets, and Alfa Bank, the country's fourth largest financial institution, U.S. officials said. But energy transactions were exempted from the latest measures, the officials said.

U.S. Treasury said transactions with Sberbank and Alfa Bank need to wind down through April 12 and May 5, respectively.

"The sanctions will not have a significant impact on the bank's operations and will not affect service to Russians as the system has already adapted to the previous restrictions," Sberbank said in a statement.

Shares in Sberbank tumbled on the Moscow Exchange after the sanctions were announced and ended the day 8.1% lower at 141.60 rubles ($1.79) per piece.

Washington said earlier on Wednesday that energy transactions will be exempted from the sanctions on Sberbank.

Alfa Bank said it will temporarily halt transactions in U.S. dollars with its counterparts but will continue transactions in rubles, euros and other currencies.

An Alfa Bank representative told Reuters it was not immediately clear what would happen to U.S. dollar accounts that its clients had with the bank.

"There have been 8,257 sanctions imposed against Russia. Previously we feared that, but now – working as usual," Alfa Bank said in a statement in its channel on the Telegram messaging service.