Police are investigating evidence of a possible arson attack at the Tesla factory near Berlin following a regional power outage that paralysed the carmaker's operations.
"We have received knowledge of a letter of confession, which we are currently examining," said a police spokeswoman on Tuesday. Its authenticity is being checked.
In an email, the left-wing extremist Vulkangruppe (Volcano group) accuses Tesla of "extreme exploitation conditions" and calls for the "complete destruction of the Gigafactory."
A burning electricity pylon caused a major power outage in the region near the factory.
Production at Tesla's only European plant in Grünheide came to a halt, and the factory was evacuated. Numerous households in the region were also affected.
"We are investigating the initial suspicion that it was deliberate arson," said the police spokesman. The State Criminal Police Office has begun an investigation.
Tesla head Elon Musk has reacted to a suspected attack on his car factory near Berlin.
"These are either the dumbest eco-terrorists in the world or they are puppets of those who don't have good environmental goals," Musk wrote social media platform X, which he owns, on Tuesday.
"Stopping production of electric vehicles, rather than fossil fuel vehicles, ist extrem dumm," the Tesla boss wrote using the German for "is extremely stupid."
German Economy Minister Robert Habeck called for a swift investigation.
"The attack on the power supply is an attack on our critical infrastructure," he said. "This must now be investigated and punished quickly. Violence and sabotage must not be a means of conflict."
The electricity pylon in question was standing freely in a field and was not fenced in. Tesla said that an arson attack was assumed and referred to information from the relevant authorities.
Tesla said that all measures had been taken to secure the production facilities. After consultation with the electricity provider EDIS, Musk's company does not expect production to restart quickly.
The state premier of Brandenburg, where the factory is located, Dietmar Woidke, warned of a form of terrorism. "This is obviously a serious attack on our critical infrastructure with consequences for thousands of people and many small and large businesses in our state," he said.
"Attacks on our critical infrastructure are a form of terrorism."
According to the police, the fire brigade was called at around 5:15 am (0415 GMT) and began extinguishing the fire.
A police helicopter was also deployed in the morning after the alarm was raised about the fire.
Earlier, a report by tabloid newspaper Bild suggested that the fire was caused by environmental activists who are occupying part of the forest that Tesla plans to use for the expansion of its factory site.
The authorities did not initially comment on a possible connection with protests around the site when asked.
Around 80 to 100 activists have been occupying part of the forest near the factory since Thursday in opposition to the company's expansion plans. The activists plan to hold out as long as possible in the 10 or so tree houses they erected.
A citizens' initiative from Grünheide is also speaking out against Tesla's expansion plans and is showing solidarity with the squatters.
Tesla has been manufacturing electric cars in Grünheide for almost two years. According to the company's latest figures, around 12,500 employees work there.
Environmentalists criticize the fact that the site is located in a water protection area, among other things. In a public consultation in Grünheide, the majority of residents said they oppose the expansion plans.
