Ukrainian drones attacked the Kirishi oil refinery in Russia's northwest, one of the country's biggest, sparking a fire when debris fell from a shot-down drone, Russian officials said on Sunday.

As big powers talk about how to end the deadliest conflict in Europe since World War Two, the drone war is heating up with Russian drones downed in NATO-member Poland and attacks by Ukraine against the oil refineries and pipelines of Russia, the world's second biggest oil exporter.

Surgutneftegaz's Kirishinefteorgsintez refinery, one of the top two refineries in Russia, was attacked by Ukrainian drones, Russian officials said.

Alexander Drozdenko, the governor of the Leningrad region, said that three drones were destroyed in the Kirishi area and that a fire sparked by falling debris had been put out. He said no one was injured.

Ukraine's drone command confirmed it attacked the refinery and said it had "carried out a successful strike."

Reuters was unable to immediately verify the scale of the damage, if any, to the refinery.

Kirishi refines about 17.7 million metric tons per year (355,000 barrels per day) of Russian crude, or 6.4% of the country's total.

Russia said that more than 80 Ukrainian drones were destroyed overnight.

An oil company in Russia's Bashkortostan region will maintain production levels despite a drone attack on Saturday, regional governor Radiy Khabirov said.