One of southern Russia’s largest oil refineries said it was struck by a Ukrainian drone attack Wednesday, setting off a massive fire.Footage published to social media showed a drone flying toward the Novoshakhtinsk refinery in the Rostov region five kilometers from the Ukrainian border before one of its facilities caught on fire."As a result of terrorist actions from the western border of the Rostov region, two unmanned aerial vehicles (UAVs) attacked the technical facilities" of the plant, the Novoshakhtinsk refinery said in a statement.It added that as a result "an explosion occurred, starting a fire."Rostov region Governor Vasily Golubev had earlier said that fragments of two drones were later found on the territory of the refinery.He added that work at the refinery has been suspended for an investigation and confirmed that there were no injuries in the incident.“Employees noticed a Ukrainian drone.

It crashed into the plant’s structures, after which there was an explosion and fire,” the state-run TASS news agencyquoted an unnamed regional official as saying.The regional Emergencies Ministry branch had reported that the fire broke out at around 9:25 a.m.

Moscow time and was extinguished within an hour and a half.It did not disclose the cause of the fire.Russia's Investigative Committee has opened a criminal case over the attack, the Kommersant business daily reported.The Novoshakhtinsk refinery is reported to be one of the largest in southern Russia with a capacity of up to 7.5 million tons per year.The latest attack follows explosions and fire at the key Transneft-Druzhba oil depot in Russia’s Bryansk region less than 100 kilometers from the Ukraine border in April.Missile strikes on Russian territory have become more common after Moscow’s forces withdrew from Kyiv in late March and Ukrainian forces' counteroffensive approached the Russian border.Several border regions have raised their terror threat levels in response to the attacks.Ukraine has not claimed responsibility for the attacks on Russian territory but has also not formally denied being behind them.  AFP contributed reporting.