BERLIN (AP) — Many households and businesses in south-west Berlin face days without electricity after high-voltage power lines were damaged by a fire which city authorities said Sunday was a result of a politically motivated attack by “left-wing extremists.”

The fire broke out on Saturday morning on a cable bridge over the Teltow Canal, near the Lichterfelde power plant, according to local authorities. Initially, over 45,000 households and 2,200 businesses in four districts were without electricity. Heating and internet services were also affected.

Franziska Giffey, the city’s Senator for Economic Affairs, described the incident as “a particularly severe power outage affecting tens of thousands of households and businesses, including care facilities, hospitals, numerous social institutions and companies.”

While power was restored to thousands of households by Sunday, many others are likely to be left in the dark until Thursday, authorities estimate.

Snowy weather and freezing temperatures has slowed down efforts to restore electricity and made life extra difficult for those affected.

The incident is being investigated as a possible act of arson. Authorities compared it to a similar power outage last September in southeast Berlin, when radical activists claimed responsibility.

Authorities said they were working to confirm the authenticity of a letter claiming responsibility for the latest incident.

The perpetrators were “clearly left-wing extremists,” Berlin’s Mayor Kai Wegner was cited as saying by a German news agency. “It is unacceptable that once again clearly left-wing extremists have attacked our power grid and thereby endangered human lives,” Wegner said.