Russia dramatically escalated its standoff with the West over the war in Ukraine on Wednesday, cutting natural gas off to NATO members Poland and Bulgaria and threatening to disconnect even more nations. European leaders decried the move as “blackmail”, writes pbs.org.

A day after the United States and other Western allies vowed to speed more and better military supplies to Ukraine, the Kremlin upped the ante, using its most essential export as leverage. The tactic could eventually force targeted nations to ration gas and deal another blow to economies suffering from rising prices. It could also deprive Russia of badly needed income to fund its war effort.

Benchmark gas prices in Europe shot up on the news that Poland and Bulgaria were cut off, marking another dark turn in a war that has revived the geopolitical rifts of the Cold War.

In a memo, state-controlled Russian giant Gazprom said it was shutting off the countries because they refused to pay in Russian rubles, as President Vladimir Putin had demanded. The company said it had not received any such payment since the beginning of the month, though Bulgaria’s energy minister disputed that.

Yet the move and Kremlin warnings that more nations could be cut off sent shivers of worry through the 27-nation European Union, which immediately convened a special coordination group to limit the impact.