BERLIN, Jan 5 (Reuters) - Berlin's mayor said on Monday the German capital's core infrastructure needed better protection two days after an arson attack on a power station left tens of thousands of people without power.

The far-left Volcano activist group claimed responsibility for the attack which also shut down mobile phone connections, cut heating during freezing weather, stopped trains and forced hospitals to switch to back-up generators.

"Left-wing terrorism is back in Germany with increasing intensity," Interior Minister Alexander Dobrindt told the Bild newspaper in an interview.

Volcano, which says it is against the energy industry's use of fossil fuels, has claimed several attacks in Berlin and the neighbouring Brandenburg region.

"There will be talks which we have to have with the federal government about how we can better protect our critical infrastructure, especially in the area of the capital," Berlin mayor Kai Wegner told a news conference.

Germany and other Western powers have also been on the alert for sabotage attacks on power, communications and transport systems at a time of increasing geopolitical uncertainty.

A blaze early on Saturday destroyed a cable duct over a canal, cutting power in around 45,000 households and more than 2,000 businesses in the southwest of the city, including the prosperous areas of Zehlendorf and Wannsee.

Electricity has since been restored for some 14,500 households but full restoration is not expected until Thursday afternoon, Stromnetz Berlin, the city's network operator, said.

In 2024, the Volcano group claimed responsibility for a suspected arson attack on a power pylon near Tesla's car factory outside Berlin.

In its most recent annual report, the domestic intelligence agency said left-wing militancy was a growing danger and made explicit reference to the Volcano group.

Bernhard Büllmann, head of Stromnetz Berlin, said restoring electricity to areas still without power would be a complex operation involving high-tension lines that required specialist staff.

(Reporting by James Mackenzie; Editing by Andrew Heavens)