The state economy minister told German media that incendiary devices had caused the damage.
Berlin’s mayor condemned the attack, accusing “suspected left-wing extremists” of knowingly endangering lives, especially those of patients in hospitals.
Hospitals and care facilities had received emergency power generators, officials said. The response had included transferring individuals from care sites and people requiring care in their own homes from the affected area to care facilities with reported available capacity.
Some hospitals had their electricity restored by Sunday.
As of Sunday afternoon, around 10,000 households and 300 businesses had been reconnected, with most still waiting to receive power back.
Some schools, which were due to reopen on Monday after the Christmas holidays, will remain closed.
The capital’s electricity operator said it would take until Thursday to reconnect all customers.
The Vulkangruppe in its statement apologised to less affluent residents impacted by the power cuts, but said it had less sympathy for “the many owners of villas”.
The statement said the attack on the gas-fired power plant was an “act of self-defence” and solidarity with those who protect the earth.
Police told AFP news agency they believed the statement was “plausible” while they continued to investigate, with other media reporting police thought it was credible.
The Vulkangruppe previously claimed responsibility for a suspected arson attack that halted production at Tesla’s Berlin car factory in 2024.