The dire threats came as Moscow claimed to have carried out a missile strike in southern Ukraine to destroy a “large batch” of Western-supplied weapons.
As the war, which has already claimed thousands of lives, entered its third month, Kyiv conceded that Russian forces had made gains in the east.
Russia’s military offensive saw it capture a string of villages in the Donbas region, now the focus target of its invasion force.
And in its economic standoff with the West, Moscow cut off gas supplies to Bulgaria and Poland, two EU and NATO members backing Ukraine in the conflict.
However Ursula von der Leyen, the president of the European Commission, said Poland and Bulgaria are now receiving gas from their EU neighbours.
She described the announcement by Russia’s state energy giant Gazprom as “another provocation from the Kremlin”.
“It comes as no surprise that the Kremlin uses fossil fuels to try to blackmail us... Our response will be immediate, united and coordinated.
“Both Poland and Bulgaria are now receiving gas from their EU neighbours,” she said. “The era of Russian fossil fuels in Europe will come to an end.”
EU officials said energy ministers from across the bloc will meet on Monday to discuss the situation.
European powers have imposed massive sanctions on Russia since Putin’s decision to invade his neighbour, while shipping weapons to Ukraine’s defenders.
But they have moved slowly on hitting Moscow’s vast exports, with many EU members—notably industrial giant Germany—reliant on Russian energy to keep their lights on.
Putin has attempted to turn up the pressure by insisting that Russia will only accept payments for gas in rubles—hoping to force his foes to prop up his currency.
Gazprom announced the halt of gas to both Poland and highly dependent Bulgaria, saying it had not received payment in rubles from the two EU members.
But von der Leyen said that “about 97 per cent” of all EU contracts explicitly stipulate payments in euros or dollars—and warned importing firms off paying in rubles.
“This would be a breach of the sanctions,” she told reporters.
The European Commission on Wednesday sought to lend Kyiv economic support by proposing a suspension of import duties on Ukrainian goods, but the idea still needs to be approved in a vote by the bloc’s 27 members.
President Zelensky welcomed the plan, adding Russia was “trying to provoke a global price crisis” and stir “chaos” in the world’s food market.
‘Destruction and painful casualties’
The first phase of Russia’s invasion failed to reach Kyiv and to overthrow Zelensky’s government after encountering stiff Ukrainian resistance reinforced with Western weapons.
The campaign has refocused on seizing the east and south of the country, while increased the use of long-range missile strikes against west and central Ukraine.
Ukraine’s Defence Minister Oleksiy Reznikov predicted “extremely difficult weeks” for the country amid “destruction and painful casualties” during the offensive.
Russia’s defence ministry said its forces had destroyed a “large batch” of weapons and ammunition supplied by the United States and European countries.
Russia hit hangars at an aluminium plant near the Ukrainian city of Zaporizhzhia with “high-precision long-range sea-based Kalibr missiles”, the ministry said.
Tensions are also rising in a breakaway region of Moldova bordering southwestern Ukraine.
In the region, Transnistria, pro-Russian separatists claimed shots were fired across the border towards a village housing a Russian arms depot, after drones flew over from Ukraine.
The unrecognised region has reported a series of explosions in recent days that it called “terrorist attacks”, leading Kyiv to accuse Moscow of seeking to expand the war further into Europe.
Moldova’s Foreign Minister Nicu Popescu called the events a “dangerous deterioration of the situation”.
Popescu said the Transnistrian authorities announced they would prevent men of fighting age from leaving the region.
Russia’s targeting of Western-supplied arms came as the United States and Europe have started to heed Zelensky’s call for heavier firepower.
Western allies remain wary of being drawn into war with Russia but have stepped up military support as Ukraine has maintained its fierce resistance.
The UN tourism body added to Russia’s isolation on the international scene as most of its 159 members on Wednesday voted to suspend it from the agency.