Brussels, Belgium (AFP) — The European Union warned Russia on Wednesday it would not bend to “blackmail” over its support for Kyiv, after the Kremlin cut off gas supplies to Bulgaria and Poland.

The warning came as UN chief Antonio Guterres arrived in Kyiv to meet Ukrainian leader Volodymyr Zelenskyy following talks with Russian President Vladimir Putin in Moscow to expand humanitarian support and secure civilian evacuations.

Putin issued his own warning on Wednesday, saying that if Western forces intervene in Ukraine, they will face a “lightning-fast” military response, after telling Guterres on Tuesday that he still hoped negotiations with Kyiv would bear fruit.

“We have all the tools for this, that no one else can boast of having,” the Russian leader told lawmakers, implicitly referring to Moscow’s ballistic missiles and nuclear arsenal.

“We won’t boast about it: we’ll use them, if needed. And I want everyone to know that,” he said. “We have already taken all the decisions on this.”

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 immediate target of its invasion force.

And in its economic stand-off with the West, Moscow cut off gas supplies to Bulgaria and Poland, two EU and NATO members backing Ukraine in the conflict.

However, later Wednesday in Brussels, 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” that would be countered.

“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 gas 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.

Moscow defended its demand that Western customers buy rubles, saying that sanctions against its central bank had forced it to rebuild its foreign reserves.

“They blocked from us — or, to put it plainly, stole — a fairly significant amount of our reserves,” Kremlin spokesman Dmitry Peskov said. “So there is no question of blackmail here.”

The first phase of Russia’s invasion failed to reach Kyiv and to overthrow President Zelenskyy’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 to counter the Western response.

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.

It also accused Ukraine of preparing to stage a fake civilian massacre in Lysychansk by disguising the bodies of dead Ukrainian soldiers in civilian clothing and taking them to the city’s central market.