Gazprom's Miller says he sees no solution to an ongoing equipment issue at part of the Nord Stream 1 pipeline.Gazprom’s Miller says he sees no solution to an ongoing equipment issue at part of the Nord Stream 1 pipeline.

European gas supplies are worried about another turbulent winter after a warning from Russia.

As a pre- summer heatwave hits western Europe this week, policymakers in the region are scrambling to fill underground storage with natural gas to keep the lights on and homes warm before the cold returns.

The risk of a full supply disruption to the EU is the reason for the fear of a severe winter gas shortage. The bloc is trying to reduce its dependence on Russian oil in response to the Kremlin.

As the conflict continues and as economic sanctions bite, the worry is just how reliable Russian gas flows will be. Russian gas supplies to several European countries have been cut due to a gas-for-rubles dispute.

Russia's Gazprom decided to further limit supplies via the Nord Stream 1 line that runs from Russia to Germany under the Baltic Sea.

The problem with the supply cut was caused by the delayed return of equipment serviced by Germany'sSiemens Energy in Canada, according to the company. Supplies from Russia have been reduced by Austria and Slovakia.

In fiery comments likely to have sent alarm bells ringing throughout the bloc, Russia will play by its own rules after halving supplies to Germany.

Our products and rules. Miller said that they don't play by rules that weren't created.

The return of equipment at the Portovaya compressor station was hampered by an unprecedented amount of economic sanctions, according to Miller. There was no solution to the problem, he said.

Flow regulator valves at a natural gas measuring station in Moldova.

Germany's Economy Minister Robert Habeck slammed Russia's supply curbs as a "political decision" designed to unsettle the region and ramp up gas prices.

Wholesale Dutch gas prices, a European benchmark for natural gas trading, jumped as much as 9% before paring gains.

The risk for European countries with high dependence on Russian gas appears to have been reinforced by the latest dispute.

EU countries may be at risk of winter energy rationing if member states don't take more steps to improve energy efficiency, according to the IEA.

The European Commission, the executive arm of the EU, said on Friday that it was aware of the announcements made by Gazprom.

The move was described as an example of blackmail by the bloc.

"Based on our exchange with the national authorities yesterday via the Gas Coordination Group, there is no indication of an immediate security of supply risk, but we will keep monitoring the situation very closely and remain in contact with the national authorities of the affected countries," they said.

It's not known when or if the gas flows will return to normal.