Russia on Thursday restored critical gas supplies to Europe through Germany via the Nord Stream pipeline after 10 days of maintenance, but suspicion lingered that the Kremlin would trigger an energy crisis on the continent this winter.

Germany, which is heavily dependent on Russian gas, had feared that Moscow would not reopen the pipeline after the scheduled work and accused Moscow of using energy as a "weapon".

The showdown came amid the worst tensions in several years over Russia's invasion of Ukraine. EU states have accused Russia of squeezing supplies in retaliation for Western sanctions over the war.

Klaus Mueller, head of Germany's energy regulator, said gas flows were on track to return to 40 percent of the pipeline's capacity -- the same reduced level as before the maintenance work.

"But given the missing 60 percent (of supply) and political instability, there is no reason to sound the all-clear," he tweeted.

German Economy Minister Robert Habeck angrily dismissed Russian claims that it was a guarantor of Europe's energy supply, saying that Moscow had become a growing "insecurity factor" in the sector.

"In fact, Russia is using the great power we gave it to blackmail Europe and Germany," Habeck of the ecologist Green party told reporters.

The Nord Stream 1 pipeline is due to reopen early Thursday after 10 days of annual repairs
The Nord Stream 1 pipeline is due to reopen early Thursday after 10 days of annual repairs AFP / John MACDOUGALL

Enduring German reliance on Russian gas coupled with alarming signals from Moscow have turned up the pressure on Europe's top economy.

A total shutdown of imports or a sharp reduction in the flow from east to west could have a catastrophic effect, shutting factories and forcing households to turn down the heat.

Even the resumption of 40 percent of supplies would be insufficient to ward off energy shortages in Europe this winter, experts warned.

"It is obvious that (Russian President Vladimir) Putin can and will turn off the tap again when it seems strategically convenient," said energy economist Lion Hirth of Berlin's Hertie School.

"We must therefore prepare for a winter without Russian gas. This means that saving gas must be at the centre of all political efforts."

The International Monetary Fund said on Wednesday that a halt in supplies could shave 1.5 percent off Germany's gross domestic product this year.

Europe waits for reopening of Nord Stream 1 gas pipeline
Europe waits for reopening of Nord Stream 1 gas pipeline AFP / Patricio ARANA

Russia's state-owned energy giant Gazprom cut flows to Germany via the Nord Stream 1 pipeline under the Baltic Sea to some 40 percent of capacity in recent weeks, blaming the absence of a Siemens gas turbine that was undergoing repairs in Canada.

The turbine is reportedly en route to Russia and expected to arrive on Sunday at the earliest. The German government has rejected Gazprom's explanation as an "excuse", noting that the turbine was one of several available.

Moscow's grounds for the supply shortfall shifted again on Thursday, as it said gas delivery problems to Europe were caused by Western sanctions.

"Any technical difficulties linked to this are caused by those restrictions that European countries introduced themselves," Kremlin spokesman Dmitry Peskov told reporters, dismissing blackmail accusations as "completely" unfounded.

Putin insisted this week that Gazprom would meet all its delivery obligations "in full".

He warned, however, that as another gas turbine was due to be sent for maintenance at the end of this month, energy flows could fall to 20 percent of capacity from next week.

As of Wednesday, German gas reserves were about 65 percent of capacity according to official estimates. Habeck said he was setting targets to boost the level to between 90 and 95 percent by November.

The European Commission on Wednesday urged EU countries to reduce their demand for natural gas by 15 percent over the coming months, and to give it special powers to force through needed demand cuts if Russia severs the gas lifeline.

Habeck, who has said he is taking shorter showers to save energy, welcomed the EU measures and rolled out a package of national policies to comply with them.

In addition to boosting its gas reserves, Germany is implementing plans to temporarily revert to more coal power, will mandate energy savings in public buildings and impose new rules for efficiency in heating homes and offices.

"We must prepare for winter," he said.

However Greece said that it was joined by Italy, Spain, Portugal, France, Malta and Cyprus in opposing the EU's plan, arguing that they were far less dependent on Russian gas than Germany.