Russia's top general said last month that Ukrainian troops had been ejected from the Kursk region, ending the biggest incursion into Russian territory since World War Two, and that Russia was carving out a buffer zone in the neighbouring Ukrainian region of Sumy.

Ukrainian forces attacked a power substation in Russia's western Kursk region, the regional governor said early on Tuesday after Russian war bloggers reported a new Ukrainian land-based incursion into the area backed by armoured vehicles.