Police in Berlin said Sunday, January 4, they suspected a far-left group of being behind an arson attack that has left tens of thousands of homes in the German capital without power.

Early on Saturday morning several high-voltage power cables were spotted in flames on a bridge near a power plant in the southwest of the city. The blaze was quickly put out, but about 45,500 households and 2,200 businesses were left without electricity.

A police spokesman told Agence France-Presse that a claim of responsibility posted online from the left-wing extremist Vulkangruppe (Volcano Group) was “plausible,” while adding that “investigations are continuing.” The statement from the Volcano Group posted online said that the power station in Berlin’s Lichterfelde district had been “successfully sabotaged” but said that “the fossil fuel economy was the target of the action, not power cuts.”

Berlin’s Mayor Kai Wegner condemned the attack, saying in a statement on X that “suspected left-wing extremists knowingly put lives at risk, especially those of patients in hospitals, as well as the elderly, children and families.”

City authorities said that most of the hospitals and clinics affected by the outage had been reconnected on Sunday. However, the affected schools are likely to remain closed for now.

Franziska Giffey, the economy minister in Berlin’s state government, told German media that “several incendiary devices” had caused the damage to the cables. She said that as of Sunday morning power had been restored to around 10,000 homes.

However, Stromnetz Berlin, which runs the city’s electricity network, said that it would take until Thursday to reconnect all customers, with freezing temperatures slowing the repair work to the cables.

The Volcano Group has previously said it was behind an act of sabotage at a Tesla factory in which power lines supplying the site were set on fire.

The German capital also suffered a major power outage affecting tens of thousands of residents in September after a blaze hit electricity pylons. Police also suspected arson in that case, and an unnamed anarchist group claimed responsibility online for starting the blaze.

Germany has been on high alert for sabotage activities directed at its infrastructure, including from foreign actors such as Russia.