German authorities have discovered 12 improvised explosive devices near two electricity substations, prompting an investigation into whether the devices are connected to a series of attacks on power infrastructure reported across the country earlier this week.

Regional authorities said on Saturday that the devices were found on Friday near high-voltage lines close to the substations at Baerwalde, near Bautzen, and Graustein, near Goerlitz, following a report from a member of the public.

Bomb disposal teams disabled the devices, while nearby electricity lines were temporarily taken offline to allow the operation to be carried out safely, police said.

Authorities are investigating a possible connection between the discoveries and the earlier attacks on electricity substations.

Germany has been rattled by a series of attacks on power infrastructure this week that appeared to target electricity supplies from coal-fired power stations and potentially cause widespread blackouts.

Authorities have described the incidents as a possible case of "climate extremism" after a 48-year-old man, identified by German media as Daniel V., reportedly sent letters claiming responsibility. Suspected explosives were also found during searches of his apartment.

The investigation intensified on Friday after the Bild tabloid reported that a heavily armed elite police unit had stormed a truck in Hambach Forest in North Rhine-Westphalia, which was suspected of belonging to the activist. The operation reportedly failed to locate him.

Hambach Forest has become a major symbol of Germany's climate movement. Activists spent years protesting plans to clear large areas of the forest to allow expansion of the nearby Hambach open-cast lignite mine.

Germany has experienced several attacks targeting its power grid in recent years, with far-left activists claiming responsibility for some of them.

The most serious incident occurred in Berlin in January, when an attack caused a major electricity outage, leaving tens of thousands of homes and thousands of businesses without power for nearly a week during the winter.