BERLIN, Jan 6, 2026 (BSS/AFP) - Anger is simmering in parts of Berlin where an arson attack claimed by a far-left group has caused a blackout that has plunged tens of thousands into icy darkness in mid-winter.

The power cut in the German capital's leafy southwest -- which has also halted local trains and forced the closure of shops, schools and hospitals -- has sparked questions about how resilient the country is to sabotage of its critical infrastructure.

Jutta Herter, 77, said she was "simply furious" with those behind the arson attack on high-voltage cables first reported Saturday morning, which left 45,000 households in the snow-covered city in the dark and many without heating.

Herter said she and her husband had lit up the fire in their bedroom -- but even this only raised the temperature to a chilly 13C.

Around her at the town hall in Zehlendorf, dozens of other residents were searching for warmth, hot drinks and electricity to charge their mobile phones, laptops and other devices.

Herter said friends had offered to put them up, but the couple wanted to stay near their home, worried about the water pipes freezing if they left the house for too long.

"You wonder what kind of people they are, what kind of feelings they have," she told AFP about the attackers. "It's unbelievable, you just can't comprehend it."

- 'Nothing ruled out' -

The arson was claimed online by an extremist group that calls itself Vulkangruppe (Volcano Group) and said it was targeting "the fossil fuel economy" driving climate change.

It follows a similar attack claimed by an anarchist group in September, when electricity pylons were set on fire, causing a blackout affecting tens of thousands in southeastern Berlin.

Germany's domestic intelligence service was checking the authenticity of the Vulkangruppe's claim of responsibility, officials said.

The arson case comes at a time when Germany, a strong backer of Ukraine, has accused Russia of a spate of "hybrid attacks", from drone overflights and espionage to online disinformation.

Conservative MP Roderich Kiesewetter has raised the possibility that Moscow was involved with the latest arson attack and the earlier one in September.

He told Welt TV that a "back-translation into Russian" of Vulkangruppe's claim of responsibility "provides a much clearer linguistic representation than the broken German one".

"So, either the far-left extremists can't speak proper German or they're being told what to say," he said, adding that "this is something that requires very intensive analysis. Nothing can be ruled out."

- 'Very dark and cold' -

Berlin emergency services, supported by the army and charity groups, were scrambling to help those affected across the Steglitz-Zehlendorf district, including care home residents who were moved to warm accommodation.

Shelter was also provided in hotels, schools and sports centres.

Around 14,500 households had been reconnected to the grid by Monday noon, said local authorities, but power was not expected to fully return to the area until Thursday.

Civil servant Philipp Pasemann, 32, was charging his phone at the town hall, wrapped in a thick coat and wearing a beanie hat.

Pasemann, who lives in a flatshare nearby, said he had managed to sleep at home so far.

"It's very cold, but I have several blankets and socks and things like that," he said.

"It's very dark and cold in the morning, but if you light candles in the evening and wrap yourself up, it's fine."

Berlin mayor Kai Wegner, weathering citizens' anger, said in a press conference that the incident had shown "once again" that "our critical infrastructure is vulnerable".

Marc Henrichmann, who chairs the parliamentary oversight committee for the intelligence services, vowed the government would "do everything in its power to combat violent extremists and enemies of our democracy".