The "era of Russian fossil fuel in Europe" is running out , the European Commission president cautioned just hours after Moscow discontinued gasoline supplies to Poland and Bulgaria.
Ursula von der Leyen said it exhibited Russia's "unreliability" as a provider.
Politicians in Warsaw and Sofia had already mentioned Russian energy giant Gazprom's move translated to "blackmail".
But the Kremlin insist Russia had been compelled into the action by the "unfriendly steps" of Western nations.
Kremlin mouth piece Dmitry Peskov added that Moscow remains a dependable energy colleague.
Gazprom's disconnection follows Poland and Bulgaria's rejection to remit payment for gas in Russian roubles - a forceful request made by President Vladimir Putin in March, which was intended to strenghten the weakening economy bashed by Western penalties.
In a declaration issued on Wednesday, Gazprom said it had "completely suspended gas supplies" to Poland and Bulgaria in line with the decree issued by Mr Putin.
The company also cautioned the countries that are conveyance states for Russian gas - that any unapproved pull out of gas approved for other European nations might perceive supplies slashed by a corresponding number.
Polish state gas company PGNiG established that Gazprom's stockpile the country had been stopped and cautioned that it reserved "the right to seek compensation".
Polish President Andrzej Duda said "appropriate legal steps" will be taken against Gazprom, while his deputy foreign minister, Marcin Przydacz, informed the BBC that Russia was seeking to "foster divisions" between Western allies.
Gazprom says Poland and Bulgaria are being picked out because they have rejected to pay for its gas in Russian roubles.
But Poland's Prime Minister Mateusz Morawiecki says slashing gas supplies is reprisal for Tuesday's declaration of Polish punishment on 50 Russian individuals and companies, including Gazprom.
Polish customers will still have hot air from their stoves this morning, but the supply slash is a critical confrontation for the rest of the year.
In the first quarter of 2022, PGNiG purchased 53% of its gas supplies from Gazprom, down from 61% all of last year. That's a lot of gas to substitute in one go.
Yes, the Polish government has triumphantly decreased its reliance on Gazprom in the past few years, by constructing a liquefied natural gas terminal in Swinoujscie - where it recieves tankers from Qatar.
But the fact remains, Poland still needs dependable substitute supplies for the rest of the year in an already constricted global market.
By the close of the year, a brand new pipeline that will permit Poland to one- on- one import gas from Norway thereby substituting Russian stockpile will be completely functional.
Bulgarian Prime Minister Kiril Petkov said the country was reconsidering all of its undertakings with Gazprom, including for passage of Russian gas to Serbia and Hungary, highlighting that "one-sided blackmail was not acceptable".
Sofia, which depends on Gazprom for more than 90% of its gas supply, said momentarily it had gotten underway to discover substitutes but there will be no restrictions on gas utilization were currently required for Bulgarians.
Ms von der Leyen, speaking in Brussels, said Gazprom's move was "unjustified and unacceptable," but emphasised that the bloc was "prepared for this scenario".
Ursula von der Leyen said the EU will assist member states affected by the gas halt.
The EU leader also lash out against reports carried by the media outlet Bloomberg which purported that 10 European energy companies are putting together to make payments for Gazprom gas in roubles, and that four energy companies have already complied.
She said such moves would be "high risk" for the corporations and would establish "a breach of our sanctions".
"Our guidance here is very clear," Ms von der Leyen said.
While the EU has been strict that it will not observe with Mr Putin's request that payments be made in roubles, Hungary has concluded a workaround deal with Gazprom.
The countries will remit into a euro-denominated account with Gazprombank, a subsidiary of the energy giant, which in turn will deposit the amount in roubles.
Mr Peskov declined so state how many other countries have consented to make remittance in this way.
Fast forward to Gazprom's declaration , Ukrainian President Volodymyr Zelensky's chief of staff charged Russia of "beginning the gas blackmail of Europe".