Russia's Gazprom halted gas supplies to Poland and Bulgaria on Wednesday over their failure to pay in rubles, a move branded as "blackmail" by the European Union (EU) chief.

The state-controlled gas pipeline giant, which supplies Europe with about 40 percent of its gas needs, said transit via Poland and Bulgaria – whose pipelines supply Germany, Hungary and Serbia – would be cut if fuel was siphoned off illegally.

Fears that more states could be hit, in particular Germany, Europe's industrial powerhouse which relied on Russia for more than 50 percent of its gas imports in 2021, sent gas prices soaring and added to jitters about the global economic impact of the conflict.

The Kremlin said the halt of natural gas supplies to Poland and Bulgaria over the refusal to pay in rubles was a result of unfriendly actions toward Russia.

"The need for a new payment method was a result of unprecedented unfriendly steps in the economic sphere and the financial sector, which were taken against us by unfriendly countries," Kremlin spokesman Dmitry Peskov told reporters on Wednesday.

European Commission President Ursula von der Leyen said in a statement on Wednesday that the "unilateral" halt from Russia is "yet another attempt by Russia to use gas as an instrument of blackmail."

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

Von der Leyen said the EU was prepared for this scenario, and would continue its work to ensure alternative supplies of gas and that gas storage is filled. The bloc's "gas coordination group" of representatives from national governments and the gas industry was meeting on Wednesday morning, she added.

Polish Prime Minister Mateusz Morawiecki also called Russia's halt "a direct attack" on Poland, adding that the EU member would not give in to "this blackmail."

He spoke after Polish state-controlled gas utility company PGNiG confirmed that Russian giant Gazprom had "completely suspended" the supply of gas to Poland via the Yamal pipeline.

"It is a direct attack on Poland... We'll deal with this blackmail, this pistol to the head in such a way that it doesn't affect Poles," said Morawiecki on Wednesday.

"Thanks to our efforts, Poland will not need Russian gas at all starting this autumn," he added. Morawiecki said on Tuesday that gas storage facilities were 76 percent full and Poland was ready to "obtain gas from all possible other directions."

(With input from Reuters, AFP)