London, Jan 21 : An explosion has occurred at a gas export terminal near the city of St Petersburg in Russia, officials say, the media reported. The blast caused a large fire, state-owned RIA Novosti news agency said. It said the fire had been contained, and there were no reports of injuries. The cause of the fire is not known, but local media have reported that drones had been seen in the area, BBC reported. Both Russia and Ukraine have used drones in the current conflict. Regional Governor Alexander Drozdenko on Sunday said a "high alert regime" was in place after the incident at the terminal of gas producer Novatek, in Ust-Luga on the Gulf of Finland. He shared a video of what appeared to be a large fire. Russian news outlet Shot quoted local residents as saying they heard a drone followed by several explosions at Ust-Luga, close to Russia's border with Estonia, BBC reported. Fontanka, a St Petersburg-based news outlet, said at least two drones were spotted flying towards the city before the fire broke out. It said there were three large international tankers near the fire, although there were no reports of damage to them, BBC reported. Russia's defence ministry also said it shot down three Ukrainian drones in Smolensk Region, close to its border with Ukraine, on Saturday night. It earlier said it had shot down drones over Tula and Oryo, both in western Russia. /IANS