Russia shut off all gas supplies to Europe through Ukraine on Wednesday - leaving more than a dozen countries scrambling to cope during a winter cold snap. Prime Minister Vladimir Putin publicly endorsed the move and urged that international observers be brought into the energy dispute. As Russia and Ukraine blamed each other for the crisis, the effects of the gas cutoff reverberated across the continent, where some countries have substantial reserves and others do not. Tens of thousands of people, mostly in Bulgaria, were without central heating. "It is a shame that in the last two decades our rulers did not look for alternative sources of energy supplies. It's again up to Moscow," retired teacher Anelia Petrova said in Sofia, Bulgaria. The EU accused both nations of using consumers as pawns in their quarrel. "It is unacceptable that the EU gas-supply security is taken hostage to negotiations between Russia and Ukraine," EU spokeswoman Pia Ahrenkilde Hansen said, demanding an immediate resumption of gas supplies. US National Security Adviser Stephen Hadley warned Moscow that using its energy exports to threaten its neighbors will undermine its international standing. Russia supplies one-quarter of Europe's natural gas, and about 80 percent of that is shipped through pipelines crossing Ukraine. Other smaller pipelines run through Belarus and Turkey. Russia's gas monopoly Gazprom stopped all gas shipments to Ukraine on January 1 after the two countries failed to agree on prices and transit fees for 2009, but kept supplies flowing to Europe over Ukraine's pipelines. Gazprom then sharply limited gas supplies moving through Ukraine on Tuesday. On Wednesday, Putin ordered Gazprom to stop all shipments of natural gas to Ukraine. "This should be done publicly and in the presence of international observers," he told Gazprom CEO Alexei Miller. As of Wednesday, nations including Bulgaria, Croatia, the Czech Republic, Greece, Italy, Macedonia, Romania, Serbia, Slovakia, Slovenia and Turkey all reported a halt in Russian gas shipments. Others - including Austria, France, Germany, Hungary and Poland - reported substantial drops in supplies. In the Balkans, people celebrating Orthodox Christmas scrambled to find other sources of heat for their homes as authorities cut off some gas to conserve supplies. Croatia announced a state of emergency, which allows it to begin rationing to industrial users. Schools and kindergartens in Bulgaria closed down as authorities tried to find alternative heating. In Bosnia, where gas operator Sarajevogas said the situation was close to a humanitarian disaster, woodcutters revved up chain saws to cut wood for fireplaces. Romania and Bulgaria held national security meetings to address the issue, while Hungary and Slovakia, which receives all of its gas from Russia, began reducing natural gas deliveries to big industrial customers. Norway, another big gas supplier to Europe, said it could not do much to offset the Russian shortfalls because it was at near-maximum production and pipeline capacity for exports. EU Commission President Jose Manuel Barroso spoke with Putin and his Ukrainian counterpart, Yulia Tymoshenko, pressing for a quick resolution to the standoff. "If this matter is not solved, it will raise very serious doubts about the reliability of Russia as a supplier of gas to Europe and Ukraine as a transit country," Barroso said. "If Ukraine is trying to be closer to the European Union, it should not create any problems when it comes to the supply of gas to the EU." He said both countries agreed Wednesday to accept international monitors to verify the flow of gas. On Thursday in Moscow, Ukraine and Russia will hold the first face-to-face talks since the breakdown of negotiations on December 31.