In a thickly forested park bordered by apartment blocks and a playground, a dozen workers were busy on a recent day with chain saws and axes, felling trees, cutting logs and chopping them into firewood to be stashed in concealed sheds around Lviv, the largest city in western Ukraine.

Ironworkers at a nearby forge are working overtime to produce wood-burning stoves to be stored in strategic locations. In municipal depots, room is being made to stockpile reserves of coal.

The activity in Lviv is being played out in towns and cities across Ukraine, part of a nationwide effort to amass emergency arsenals of backup fuel and critical provisions as Russia tightens its chokehold on energy supplies across Europe.

curtailed gas supplies to Europe last week, leading the European Union to announce that it will reduce imports of Russian gas so as not to be held hostage. Russia turned off the gas taps to Latvia on Saturday, after the government there announced additional military assistance for Ukraine, the latest in a string of European countries to do so.

Ukraine buys its natural gas from European neighbors, so the restriction of deliveries to Europe threatens its access to energy, too.

ordered to evacuate this past weekend after months of relentless Russian bombardment destroyed the infrastructure needed to deliver heat and electricity.

“We understand that the Russians may continue targeting critical energy infrastructure before and during the winter,” said Oleksiy Chernyshov, Ukraine’s minister for communities and territories development, in an interview.

“They’ve demolished central heating stations in big cities, and physical devastation is still happening nationwide,” he said. “We are working to repair damage, but it doesn’t mean we won’t have more.”

Far from Ukraine’s embattled southeastern front, the campaign is being waged in forests and in steel forges, at gas storage sites and electrical stations, and even in basement boiler rooms, as the government mobilizes regions to activate a blueprint for amassing fuel and shelter.

disconnect Ukraine’s energy grid from Russia and Belarus and link it directly to the European Union’s. Last month, Ukraine began exporting small amounts of electricity to Romania, with hopes of eventually supplying European companies that have been hit by Russian natural gas cuts, a potential source of valuable income.

But Ukrainian officials say the ability to supply electricity at home, especially over the coming winter, when temperatures can fall far below freezing, is increasingly threatened as Russia intensifies a campaign of targeting the infrastructure that delivers energy.

Russian shelling has hit thermal power plants around the country and over 200 gas-fired boiler plants used for centralized heating. Around 5,000 kilometers of gas pipelines have been damaged, along with 3,800 gas distribution centers, according to an analysis by the Woodrow Wilson International Center’s Kennan Institute, a think tank focused on Russia.

Gas is especially critical for Ukraine because it is used to warm thousands of high-rise apartment complexes, schools, post offices and municipal buildings that rely on centralized heating systems.