Russia has halted gas deliveries to Germany via a key pipeline an indefinite period after saying Friday it had found problems in a key piece of equipment, a development that will worsen Europe's energy crisis.

Russian gas giant Gazprom said Friday that the Nord Stream pipeline due to reopen at the weekend would remain shut until a turbine is repaired.

In a statement, Gazprom indicated it had discovered "oil leaks" in a turbine during a planned three-day maintenance operation.

Gazprom added that "until it is repaired... the transport of gas via Nord Stream is completely suspended".

Resumption of deliveries via the pipeline which runs from near St Petersburg to Germany under the Baltic Sea, had been due to resume on Saturday.

Gazprom said it had discovered the problems while carrying out maintenance with representatives of Siemens, which manufactured the turbine in a compressor station that pushes gas through the pipeline.

On its Telegram page it published a picture of cables covered in a brown liquid.

Earlier in the day, the Kremlin warned the future operation of the Nord Stream pipeline, one of Gazprom's major supply routes, was at risk due to a lack of spare parts.

"There are no technical reserves, only one turbine is working," Kremlin spokesman Dmitry Peskov told reporters.

"So the reliability of the operation, of the whole system, is at risk," he said, adding that it was "not through the fault" of Russian energy giant Gazprom.

Following the imposition of economic sanctions over the Kremlin's invasion of Ukraine, Russia has reduced or halted supplies to different European nations, causing energy prices to soar.

The Kremlin has blamed the reduction of supplies via Nord Stream on European sanctions which it says have blocked the return of a Siemens turbine that had been undergoing repairs in Canada.

Germany, which is where the turbine is located now, has said Moscow is blocking the return of the critical piece of equipment.

Berlin has previously accused Moscow of using energy as a weapon.

The announcement by Gazprom comes the same day as the G7 nations said they would work to quickly implement a price cap on Russian oil exports, a move which would starve the Kremlin of critical revenue for its war effort.

Gazprom also announced the suspension of gas supplies to France's main provider Engie from Thursday after it failed to pay for all deliveries made in July.

As winter approaches, European nations have been seeking to completely fill their gas reserves, secure alternative supplies, and put into place plans to reduce consumption.

A long-term halt to Russian gas supplies would complicate efforts by some nations to avoid shortages and rationing, however.

Germany said Friday its gas supplies were secure despite the halt to deliveries via Nord Stream.

"The situation on the gas market is tense, but security of supply is guaranteed," a spokeswoman for the economy ministry said in a statement.

The spokeswoman did not comment on the "substance" of Gazprom's announcement earlier Friday but said Germany had "already seen Russia's unreliability in the past few weeks".

German officials have in recent times struck a more positive tone about the coming winter.

Before the latest shutdown, Chancellor Olaf Scholz said Germany was now "in a much better position" in terms of energy security, having achieved its gas storage targets far sooner than expected.

Europe as a whole has also been pushing ahead with filling its gas storage tanks, while fears over throttled supplies have driven companies to slash their energy usage.

Germany's industry consumed 21.3 percent less gas in July than the average for the month from 2018 to 2021, said the Federal Network Agency.

Agency chief Klaus Mueller has said such pre-emptive action "could save Germany from a gas emergency this winter".

Europe as a bloc meanwhile has been preparing to take emergency action to reform the electricity market in order to bring galloping prices under control.

Fear of shortages of natural gas has driven futures contracts for electricity in France and Germany to record levels.

European consumers are also bracing for huge power bills as utilities pass on their higher energy costs.