Two Russian oil facilities were damaged by suspected drone attacks on Thursday.
The Gazprom Neftechim Salavat refinery in the city of Salavat in the Urals was hit, according to the head of the Russian Republic of Bashkortostan, Radiy Khabirov.
According to Russia's Interfax news agency, smoke could be seen in one part of the plant. Local rescue workers said that one of the plant's pumping stations was damaged.
Russian officials did not say whether the attacking drone came from Ukraine.
Salavat is located around 1,400 kilometres as the crow flies from the nearest possible launch sites in Ukraine. However, Ukrainian forces have greatly increased the range of their drones in recent months amid the fight against Russia's ongoing invasion.
There have been a number of previous attacks on oil facilities deep in the Russian hinterland.
An oil storage facility on the Russian Black Sea coast near the city of Anapa also caught fire, with local authorities assuming it was the result of a Ukrainian drone attack.
Around six approaching combat drones were intercepted overnight, but some of them fell on the tank farm.
A fire broke out, which was brought under control around midday. Several tanks were damaged. The distance from Anapa to Ukrainian-controlled territory is around 370 kilometres.