Natural gas prices have risen in Europe as a sharp cut in supplies to Russia is slowing the rate at which storage is being filled, which could lower the levels needed to heat homes this winter.

Benchmark futures started the week up as much as 6.9%. It has become more difficult for buyers to replace Russian gas from other countries after earlier this month its main supplier cut off 60% of gas flows along the main route to Europe by 60%.

The situation could only get worse as the Nord Stream gas pipeline, the largest link from Russia to the European Union, is scheduled to be completely shut down for maintenance next month. German Economics Minister Robert Habeck said he could not be sure Russia would resume deliveries via the canal once work is completed, raising the possibility of another price spike and rationing this winter.