Andrei Bocharov, the governor, said in a statement on the Telegram messaging app that Russian air defences had repelled an attack on his region by eight drones.
"As a result of falling debris from one of the drones, a fire broke out on the territory of an oil refinery, which was promptly extinguished. One injured refinery worker was hospitalised," he said.
Andriy Kovalenko, the head of Ukraine's Centre for Countering Disinformation, said on Telegram the Volgograd oil refinery, which he described as one of Russia's largest, had been struck.
SHOT, a Russian news outlet with contacts in the security services, said four Ukrainian drones had been destroyed over a second refinery in Yaroslavl, northeast of Moscow.
Lukoil has denied one its Russian refineries was hit and said production was unaffected. (EPA PHOTO)
Ukraine has carried out frequent air attacks on Russian refineries, oil depots and industrial sites in an attempt to cripple key infrastructure underpinning Russia's war effort.
This week it claimed to have struck and set on fire a Lukoil refinery, Russia's fourth largest, in the Nizhny Novgorod region, east of Moscow.
Sources at Lukoil denied that the NORSI refinery was hit, and said production was not affected. Petrochemical company Sibur said there had been a drone strike and fire at its nearby plant.
Russia is currently feeding more crude oil through its refineries in the hope of boosting fuel exports after new US sanctions on Russian tankers and traders made exports of unprocessed crude more difficult, sources told Reuters this week.
A Ukrainian drone attack last week forced a refinery in Ryazan, southeast of Moscow, to suspend operations.
Russia's Defence Ministry said in a statement on Friday that 49 Ukrainian drones had been downed over the country overnight, including 25 in the southern Rostov region and eight in the Volgograd region.
Drones had also been detected and destroyed in the Kursk, Yaroslavl, Belgorod, Voronezh, and Krasnodar regions, it said.
Russian drones caused damage in the northeastern Sumy region overnight. (EPA PHOTO)
Meanwhile, Russia launched a barrage of drones on Ukraine in an overnight attack, injuring four people and damaging a hospital and a grain warehouse in the southern Odesa region, officials said.
Ukraine's air defences shot down 59 of 102 Russian drones, the air force said. It said that 37 drones were "lost", referring to the use of electronic warfare to redirect them.
Russian drones caused damage in the northeastern Sumy region, the Odesa region in the south and the central Cherkasy region.
Oleh Kiper, the Odesa regional governor, said four civilians, including a doctor, were injured in drone attacks targeting the city of Chornomorsk.
The strikes also partially disrupted electricity supplies in the city and damaged the city's hospital, an administrative building, a grain warehouse, a residential house, and several trucks, he said on the Telegram app.
Regional officials in the central Cherkasy region said that drone debris damaged an apartment building in the region.
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