The Orenburg plant, run by state-owned gas giant Gazprom and located in a region of the same name near the Kazakh border, is part of a production and processing complex that is one of the world's largest facilities of its kind, with an annual capacity of 45 billion cubic meters.
It handles gas condensate from Kazakhstan's Karachaganak field, alongside Orenburg's own oil and gas fields.
According to regional Governor Yevgeny Solntsev, the drone overnight strikes set fire to a workshop at the plant and damaged part of it.
The Kazakh energy ministry on Sunday said, citing a notification from Gazprom, that the plant is temporarily unable to process gas originating in Kazakhstan, "due to an emergency situation following a drone attack."
Ukraine's General Staff said in a statement that a "large-scale fire" erupted at the Orenburg plant, and that one of its gas processing and purification units was damaged.
Kyiv has ramped up attacks in recent months on Russian energy facilities it says both fund and directly fuel Moscow's war effort.
Meanwhile, Ukrainian prosecutors claim that Moscow is modifying its deadly aerial-guided bombs to strike civilians deeper in Ukraine. Local authorities in Kharkiv said Russia struck a residential neighbourhood using a new rocket-powered aerial bomb for the first time.
Kharkiv's regional prosecutor's office said in a statement late Saturday that Russia used the weapon, called the UMPB-5R, which can travel up to 130km, in an attack on the city of Lozava on Saturday afternoon. The city lies 150km south of Kharkiv, a considerable distance for the weapon to fly.
Russia continued to strike other parts of Ukraine closer to the front line. In the Dnipropetrovsk region, at least 11 people were injured after Russian drones hit the Shakhtarske area. At least 14 five-story buildings and a store were damaged, said acting regional Governor Vladyslav Haivanenko.
Ukraine's General Staff also claimed a separate drone strike hit Russia's Novokuibyshevsk oil refinery, in the Samara region near Orenburg, sparking a blaze and damaging its main refining units.
The Novokuibyshevsk facility, operated by Russian gas major Rosneft, has an annual capacity of 4.9 million tons, and turns out over 20 kinds of oil-based products. Russian authorities did not immediately acknowledge the Ukrainian claim or discuss any damage.
Russia's Defense Ministry said in a statement early Sunday that its air defence forces had shot down 45 Ukrainian drones during the night, including 12 over the Samara region, one over the Orenburg region and 11 over the Saratov region neighbouring Samara.
In turn, Ukraine's air force reported Sunday that Russia during the night launched 62 drones into Ukrainian territory. It said 40 of these were shot down, or veered off course due to electronic jamming.
