Ukraine said it hit the Ilskaya oil refinery in Russia's Krasnodar region overnight, Ukrinform and Reuters reported, quoted by BTA.
Krasnodar region authorities said three people were killed and two were injured in the attack.
Local residents reported explosions and the activation of air defense systems, as well as a subsequent fire at the refinery.
The refinery can process about 6.6 million tons of oil per year, and has six main processing units. The Il'sk refinery is one of the leading oil refineries in southern Russia, and its output is used, among other purposes, to supply the Russian armed forces. Crude oil is supplied through the Transneft pipeline system.
Meanwhile, the Russian Defense Ministry said that a total of 645 drones were shot down over various Russian regions overnight.
A facility in the Russian city of Ulyanovsk, which is involved in the production of guided aircraft missiles, was hit last night. Two facilities in the Tula and Voronezh regions, where rocket fuel is produced, were also hit, Ukrinform notes.