(Bloomberg) -- Russia launched an overnight drone strike on the northeastern Ukrainian Sumy region, where authorities in Kyiv have braced for a potential new front in the war. 

The attack, which damaged energy facilities and triggered blackouts in the city of Sumy, was carried out northwest of Kharkiv, where Kremlin troops opened a fresh front this month to put pressure on Ukraine’s increasingly fragile defenses. The power supply was partially restored by early Wednesday, the utility and local regional authority said. 

As Ukraine’s military dispatches troops to Kharkiv to stave off the Russian advance, President Volodymyr Zelenskiy has also warned of Russian activity in the neighboring regions of Sumy and Chernihiv, including shelling and sabotage operations. Ukraine’s military intelligence chief, Kyrylo Budanov, said earlier this month that Moscow was stationing units along the border near Sumy. 

Ukrainian forces grappling with a shortage of ammunition and manpower after a months-long delay of new US materiel are trying to hold off Russia’s momentum. Authorities have said the Kremlin is seeking to draw off Ukrainian troops from other parts of the front line — though haven’t amassed enough to mount an assault to take Kharkiv, Ukraine’s No. 2 city. 

Russia has increased attacks this year on thermal and hydro power plants with missile and drone barrages, destroying about half of Ukraine’s energy system. That’s forced Kyiv to import electricity from the European Union and implement scheduled power cuts to balance the system.

The shortage of electricity nationwide will continue in the coming months, and at times emergency imports from the EU won’t be enough to overcome the generation shortfall, Ukrenergo Chief Executive Officer Volodymyr Kudrytski said in televised remarks late Tuesday. Power companies now need to focus preparations for the next heating season, he said.

Energy infrastructure was damaged in the towns of Shostka and Konotop in the Sumy region, according to statements by the grid operator Ukrenergo and the Sumy regional military administration on Telegram. Konotop is about 240 kilometers (150 miles) east of Kyiv. 

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