NATO member and staunch Kremlin opponent Poland is among the European countries seeking the toughest possible sanctions against Russia for its invasion. Fellow alliance member Bulgaria is almost completely reliant on Russian gas imports.
Poland's state-owned PGNiG said supplies from energy giant Gazprom via Ukraine and Belarus would be cut on Wednesday, but Warsaw said it did not need to draw on reserves and its gas storage was 76 per cent full.
"The gas system in Poland is balanced and customers can feel safe," Minister in Charge of Energy Security Piotr Naimski said.
Russian President Vladimir Putin has called on "unfriendly" countries to pay for gas imports in roubles, a move only a few buyers have implemented so far.
Gazprom said it had not suspended supplies to Poland but that Warsaw had to pay for gas from it in line with its new "order of payments". It declined to comment regarding Bulgaria.
Andriy Yermak, the chief of staff to Ukrainian President Volodymyr Zelenskiy, said Russia was "beginning the gas blackmail of Europe".
"Russia is trying to shatter the unity of our allies. Russia is also proving that energy resources are a weapon. That is why the EU needs to be united and impose an embargo on energy resources, depriving the Russians of their energy weapons."
Russia's invasion of Ukraine, launched on February 24, has left thousands dead or injured, reduced towns and cities to rubble, and forced more than 5 million people to flee abroad.
Moscow calls its actions a "special operation" to disarm Ukraine and protect it from fascists. Ukraine and the West call this a false pretext for an unprovoked war to seize territory.
Russia's ambassador to the United States has warned Washington to stop sending arms to Ukraine, saying that large Western deliveries of weapons were inflaming the situation.
Russian foreign minister Sergei Lavrov warned on Monday that: "NATO, in essence, is engaged in a war with Russia through a proxy and is arming that proxy. War means war," saying the risks of nuclear conflict should not be underestimated.
US Pentagon spokesman John Kirby said there was no reason for the conflict in Ukraine to escalate to nuclear war. "A nuclear war cannot be won and it shouldn't be fought," he said.
Ukraine also accused Moscow on Tuesday of trying to drag Moldova's breakaway region of Transdniestria into the conflict after authorities in the Moscow-backed region said they had been targeted by a series of attacks.
The Kremlin, which has troops and peacekeepers in the region, said it was seriously concerned.
Meanwhile, fighting continued in eastern and southern Ukraine.
Russia's defence ministry said its forces had "liberated" the entire Kherson region in southern Ukraine and parts of the Zaporizhzhia, Mykolaiv and Kharkiv regions, Interfax news agency reported.
If confirmed, that would represent a significant Russian advance.
US Defense Secretary Lloyd Austin, welcoming officials from more than 40 countries to Ramstein Air Base in Germany, said: "Nations from around the world stand united in our resolve to support Ukraine in its fight against Russia's imperial aggression."
The talks on Tuesday sought to speed and synchronise the delivery of arms to Kyiv.
Germany, which had come under pressure after refusing Ukrainian pleas for heavy weapons, announced it would send Gepard light tanks with anti-aircraft guns.
United Nations Secretary-General Antonio Guterres, in Moscow on Tuesday, made a proposal on how to evacuate people from the besieged Ukrainian city of Mariupol, involving a "Humanitarian Contact Group" of Russia, Ukraine and UN officials.
Ukraine said no corridors were operating on Tuesday due to continued fighting.
The United Nations said Putin had agreed "in principle" during talks with Guterres to UN and Red Cross involvement in evacuating civilians from the Azovstal steel plant in Mariupol, scene of the worst fighting of the war.
