Officers confirmed the find of "an unexploded incendiary device," while plant operator Leag called it "an attack."
According to German newspaper Märkische Allgemeine Zeitung, a 500-megawatt generating unit was taken offline, but the wider blackout apparently intended at the plant did not occur.
Meanwhile, grid operator 50Hertz said unknown perpetrators had briefly disrupted several lines before service was restored, with no effect on overall supply.
Brandenburg's interior and energy ministers travelled to the region, and Infrastructure Minister Robert Crumbach described it as an assault on public safety and energy security.
No injuries have been reported, and no suspects have yet been identified.
Jänschwalde is the largest power plant of its kind in the state, with an installed capacity of 1,500 megawatts, according to the operator.
(ał/gs)
Source: IAR, tvp.info, maz-online.de