Berlin — An arson attack claimed by a left-wing extremist group has left tens of thousands of residents in Germany's capital without electricity in the dead of winter for several days. The Saturday morning arson attack on critical electricity infrastructure in southwest Berlin cut power to nearly 50,000 homes and businesses, and renewed scrutiny of a long-running sabotage campaign by the left-wing "Vulkangruppe."

The group claimed responsibility for the fire, which destroyed several high-voltage cables near the Lichterfelde heat and power station and triggered one of the most severe blackouts the capital has experienced in years.

According to Stromnetz Berlin, the operator of Berlin's electricity network, power was cut to as many as 45,000 households and more than 2,000 businesses across four districts in south Berlin. 

The power outage also meant many homes lost heating and hot water as temperatures dropped well below freezing in Berlin. 

While engineers restored power to parts of the network by Monday, about 30,000 households were still offline as technicians struggled to replace damaged underground cables buried in the frozen soil. The power operator said it didn't expect to have electricity fully restored until Thursday.

In a lengthy statement circulated online and called credible by police, the Vulkangruppe said it had deliberately targeted affluent neighborhoods, to "cut the juice to the ruling class." 

The group framed the attack as an act of protest against fossil fuel energy use and the growing power demand created by AI data centers, which it said had accelerated climate change and expanded mass surveillance. The statement included an apology to less wealthy residents caught up in the blackout but it expressed no sympathy for wealthy homeowners left without electricity.

The impact of the attack quickly spread beyond the areas the group said it had intended to target. Hospitals, care homes for the elderly and high-rise building residents who rely on elevators were impacted. Cell phone networks failed in some districts and commuter rail services were disrupted. Police used loudspeakers mounted on patrol cars to inform residents, and some schools delayed reopening after the Christmas and New Year's holiday break.

Berlin Mayor Kai Wegner condemned the arson attack as an "absolutely unacceptable" act of terrorism. He warned that assaults on energy infrastructure endangered lives and placed enormous strain on the city's emergency services.

"These are not childish pranks, but rather professional criminals who attacked these power grids," Wegner said in an interview Monday with German public broadcaster RBB. "This is not just arson or sabotage. This is already terrorism. It was a left-wing extremist group that once again attacked our infrastructure and, in doing so, also endangered the lives of people, of elderly people who may need ventilators, of families with small children, and we now have to catch these perpetrators."

Franziska Giffey, the Berlin state's Senator for Economic Affairs, Energy, and Public Enterprises, asked the federal government to help with the criminal investigation into the extremist group's actions, which she called an attack on "our free society."

"It must be about federal assistance in the investigations," she said. "The question is whether these are merely left-wing activist groups acting out of ideological motives, or whether there is more behind it."

Security officials said the arson fit a pattern that's been developing for more than a decade. According to assessments by Berlin authorities and Germany's domestic intelligence services, groups using the name Vulkangruppe or closely related labels have been responsible for a series of attacks on power, rail and communications infrastructure since about 2011. 

Early incidents included arson attacks on rail and electricity cables in Berlin that disrupted commuter traffic and caused costly damage. In 2018, a fire set on power lines cut electricity to thousands of households and businesses in the capital, while later attacks targeted research and communications facilities linked to digital infrastructure.

The group has gained more attention in recent years through increasingly high-profile actions. In March 2024, it claimed responsibility for an arson attack on a high-voltage pylon supplying electricity to the Tesla Gigafactory Berlin-Brandenburg, temporarily halting production at the plant.

In September, another arson attack on power cables in southeast Berlin caused a 60-hour blackout affecting tens of thousands of residents, reportedly the longest power cut in the city since World War II. It was widely attributed to the same extremist collective, though not claimed explicitly by the Vulkangruppe.

Authorities warn that such attacks require little specialist knowledge but can have dramatic and far-reaching consequences, exposing vulnerabilities in densely interconnected urban infrastructure. 

The latest blackout has intensified calls for stronger protection of power grids and plans for faster emergency responses to such incidents.