An extreme left-wing group claimed responsibility for an arson attack that caused a blackout affecting about 45,000 households and more than 2,000 businesses in Berlin over the weekend, Politico reported Monday.

“This isn't just arson or sabotage. It's terrorism,” Berlin Mayor Kai Wegner said of the attack, which burned through a cable connected to one of the city’s largest gas-fired power plants.

Members of the so-called Vulkan Group, known for similar attacks on critical infrastructure, claimed responsibility in an online letter titled “Cutting off power to those in power,” denouncing “greed for energy” and saying the aim was to damage the gas industry.

Listed by Berlin’s intelligence services as a left-wing extremist organization, the group has used similar communications before, and police believe the letter to be genuine.

With temperatures below freezing, schools and kindergartens in affected southern districts remained closed Monday.

Around 30,000 households and approximately 1,700 businesses were still without power on the third day, with full restoration expected by Thursday.

Berlin’s energy senator, Franziska Giffey, questioned whether the perpetrators were acting purely on ideology or if “there is more to it than that,” calling the attack not only on infrastructure but “also an attack on our free society.”