European Commission President Ursula von der Leyen said on Wednesday that Russia's decision to cut gas supplies to two European Union members, Poland and Bulgaria, is "another attempt by Russia to blackmail us with gas."

"This is unjustified and unacceptable," she said in a statement. "And it shows once again the unreliability of Russia as a gas supplier."

Von der Leyen said EU countries had prepared contingency plans for a gas shutdown, and that a meeting of the bloc's gas coordination group of national authorities and energy agencies was taking place "right now."

"We are mapping out our coordinated EU response. We will also continue working with international partners to secure alternative flows," she said.

The Bulgarian Prime Minister Kiril Petkov said that von der Leyen told him that "Gazprom's breach of contract is a problem for all of the EU, and that the EU will have common response."

European gas prices have surged by more than 20 percent as a consequence of Russia's halting gas flows to Poland and Bulgaria.

Gas deliveries should be suspended to unfriendly countries that refuse to pay for fuel in rubles, said Vyacheslav Volodin, chairman of Russia's lower parliament house the State Duma, on Wednesday.