Russian gas currently accounts for about 8% of Europe’s supply. The Ukrainian transit route served EU members Austria and Slovakia, which long got the bulk of their natural gas from Russia but have recently scrambled to diversify supplies.

Gazprom halted supplies to Austria’s OMV in mid-November over a contractual dispute, but gas flows through Ukraine’s pipelines continued as other customers stepped in.

Slovakia this year inked deals to begin buying natural gas from Azerbaijan, and also to import U.S. liquefied natural gas through a pipeline from Poland.

Natural gas is used to generate electricity, power industrial processes, and in some cases to heat homes.