The fire affected industrial equipment at the Novoshakhtinsk oil refinery in the Rostov-on-Don region. Authorities said dozens of firefighters extinguished the blaze within half an hour and no one was injured.
The refinery said in a statement that the fire was caused by two drones, calling it a “terrorist” act.
He did not give further details, but the state-run Tass news agency said two Ukrainian drones had flown over the plant and one of them had hit a heat exchanger, setting it on fire.
Ukrainian officials have not claimed responsibility for the drone strike.
A video posted on a messaging application channel showed a drone flying and hitting what was supposed to be a refinery, a giant column of smoke rising into the sky.
The authenticity of the video could not be independently verified.
Rostov-on-Don regional governor Vassily Golubev said fragments of two drones had been found on the factory grounds.
The refinery said it had temporarily suspended work to assess the damage.
Wednesday’s attack on the refinery follows a series of explosions and fires in western Russia amid Moscow’s clashes in Ukraine in an operation that began almost four months ago.
In April, two Ukrainian helicopters struck an oil depot in Belgorod, according to Russian officials, causing a massive fire.
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Several other explosions and fires hit refineries, oil depots and an ammunition storage facility. Ukraine has not officially claimed responsibility for the incidents, but some Ukrainian media have praised them as a result of the Ukrainian raids.