Russia's Gazprom halted gas supplies Wednesday to Poland and Bulgaria, the latest step in the economic fight linked to Russia's invasion of Ukraine.
Russia has demanded that European nations, many of which rely on Russia for large portions of their energy supplies, pay for natural gas in rubles, Russia's currency.
Gazprom said Wednesday that Poland and Bulgaria had not done so and would therefore have their gas supplies suspended.
Polish and Bulgarian officials said the Gazprom move amounted to a breach of contract.
Polish President Andrzej Duda said the Russian gas cutoff violated "basic legal principles," while Bulgarian Energy Minister Alexander Nikolov said gas was being used as a "political and economic weapon."
On Twitter, European Union Commission President Ursula von der Leyen said, "It comes as no surprise that the Kremlin uses fossil fuels to try to blackmail us. This is something the EU Commission has been preparing for, with Member states and international partners. Our response will be immediate, united and coordinated."
Several EU nations have moved to lessen or eliminate their dependence on Russian energy, including by seeking other sources and boosting their use of renewable energy.
Meanwhile, Russia's Defense Ministry said Wednesday its forces carried out missile strikes overnight that destroyed 59 targets in Ukraine, including "hangars with a large batch of foreign weapons and ammunition" sent by the United States and European countries to aid Ukraine's military.
The United States and its allies signaled Tuesday they are moving swiftly and powerfully to support Ukrainian forces and escalate pressure on Russia's economy.
The United States at first "needed weeks" to move military equipment and munitions to Ukraine, Secretary of State Antony Blinken told the Senate Foreign Relations Committee, but it now often dispatches new armaments to the Ukrainians within three days.
Blinken said since he and Defense Secretary Lloyd Austin met with Ukrainian President Volodymyr Zelenskyy in Kyiv over the weekend, the two countries were "largely aligned in what they say they need and what we think we're able to provide."
Germany's government said Tuesday it would send heavy weapons to Ukraine for the first time. Austin, meeting at a U.S. air base in Germany with officials from 40 countries, including NATO members, said Russian President Vladimir Putin "never imagined the whole world would rally behind Ukraine so swiftly and surely."
"We're seeing more support every day" to combat the Russian invasion, he said Tuesday. "We don't have any time to waste. We've got to move at the speed of war."
The White House said Germany's decision signaled unprecedented unity in the face of Russian aggression.
"The announcement by Germany is in line with announcements we've seen by a number of European countries in providing assistance they have never before provided, which is part of the significance here," White House press secretary Jen Psaki told reporters.
"So, this is an unprecedented change to provide lethal aid to another country, and that's the significance here from Germany. But I'd also note that Norway provided Mistral anti-aircraft missiles, that a number of countries have provided types of assistance that they have never done in the past, and that really speaks to the significant unity of NATO."
Defense Secretary Austin said allies supporting Ukraine would meet monthly to coordinate further aid. As he opened the talks, he said the aim was to "help Ukraine to win the fight against Russia's unjust invasion and to help build up Ukraine for tomorrow's challenges."
Austin also rebuked Russian Foreign Minister Sergey Lavrov for suggesting that the war could evolve into a nuclear conflict between Russia and the West.
"We certainly will do everything in our power … to make sure it doesn't spin out of control," Austin said. "Nobody wants to see a nuclear war. Nobody can win it," he said, adding that "it's unhelpful and dangerous to rattle sabers" over a nuclear threat.
Austin's appeal to allies for more help for Ukraine came a day after he said the U.S. objective in supporting Ukraine was to leave Russia with a "weakened" military. He described Russian casualties so far as "pretty substantial," with some military analysts saying as many as 20,000 Russian troops have died.
Moscow accused the West of carrying out a proxy war against Russia by sending more munitions to Ukraine and warned of a "considerable" risk that the fighting could evolve into a nuclear conflict.
United Nations Secretary-General Antonio Guterres met Tuesday in Moscow with Putin and Lavrov in an attempt to broker a cease-fire agreement, even as Russia launched new attacks on eastern and southern Ukraine. Guterres then headed to Ukraine, stopping first in Poland to meet with that nation's president in a city along the Ukrainian border used as a base for American troops and humanitarian efforts.
During the two-hour meeting with Guterres in the Russian capital, Putin agreed "in principle" to allow the U.N. and the International Committee of the Red Cross to assist with the evacuation of civilians from the Azovstal iron and steel plant in Mariupol, Guterres spokesman Stephane Dujarric said.
The U.N. chief said that while Russia and the U.N. had "different interpretations of what's happening in Ukraine," there was still the possibility for a serious conversation about working to minimize suffering and "end the war as soon as possible."
Also on Tuesday, State Department spokesman Ned Price said American diplomats have taken concrete steps to reestablish a U.S. diplomatic presence in Ukraine.
"I can confirm that the deputy chief of mission and members of the embassy team traveled to Lviv, Ukraine, today, where they were able to continue our close collaboration with key Ukrainian partners," he said. "Today, they met with interlocutors from the Ukrainian Ministry of Foreign Affairs."
VOA's Anita Powell and Ken Bredemeier contributed to this report. Some information came from The Associated Press, Reuters and Agence France-Presse.