Russia has cut off natural gas to Nato members Poland and Bulgaria and threatened to do the same to other countries, dramatically escalating its standoff with the West over the war in Ukraine. European leaders decried the move as “blackmail”.

A day after the US and other Western allies vowed to speed more and heavier weapons to Ukraine, the Kremlin used its most essential export as leverage against two of Kyiv’s staunch backers. Gas prices in Europe shot up on the news.

The tactic could eventually force targeted nations to resort to gas rationing and could deal another blow to economies suffering from rising prices. At the same time, it could deprive Russia of badly needed income to fund its war effort.

Western leaders and analysts portrayed the move by the Kremlin as a bid to both punish and divide the allies so as to undermine their united support for Ukraine.

Poland has been a major gateway for the delivery of weapons to Ukraine and confirmed this week that it is sending the country tanks. It has also been a vocal proponent of sanctions against the Kremlin.

Bulgaria, under a new liberal government that took office last fall, has cut many of its old ties to Moscow and likewise supported punitive measures against Russia. It has also hosted Western fighter jets at a new Nato outpost on its Black Sea coast.

The gas cuts do not immediately put the two countries in any dire trouble. Poland, especially, has been working for many years to line up other suppliers, and the continent is heading into summer, making gas less essential for households.

Yet the cutoff and the Kremlin warning that other countries could be next sent shivers of worry through the 27-nation European Union. Germany, the largest economy on the continent, and Italy are among Europe’s biggest consumers of Russian natural gas, though they have already been taking steps to reduce their dependence on Moscow.

“It comes as no surprise that the Kremlin uses fossil fuels to try to blackmail us,” said EU Commission president Ursula von der Leyen. “Today, the Kremlin failed once again in its attempt to sow division amongst member states. The era of Russian fossil fuel in Europe is coming to an end.”

State-controlled Russian giant Gazprom said it was shutting off the two countries because they refused to pay in rubles, as President Vladimir Putin has demanded of “unfriendly” nations. The Kremlin said other countries may be cut off if they don’t agree to the payment arrangement.