Austria has insisted it is well prepared for the stoppage, but Slovakia has threatened to cut electricity supplies to neighboring Ukraine.

The Urengoy-Pomary-Uzhgorod pipeline was built in the Soviet era to carry Siberian gas to European markets. It became the main conduit to Ukraine’s border with Slovakia from Siberia, passing through the town of Sudzha — which is now under the control of Ukrainian military forces — in Russia’s Kursk region.