Ukraine said it used long-range drones on the night of 5 August to strike two oil refineries inside Russia, including the large Slavneft-YANOS refinery in Yaroslavl Oblast, which it said was hit for a second straight night, and a smaller refinery in the Bashkortostan Republic.
President Volodymyr Zelensky said the Bashkortostan refinery is about 1,300 km from the front line.
Videos posted by residents showed a large fire at the Yaroslavl refinery, located more than 700 km from the Ukrainian border; damage there could not be independently verified.
Yaroslavl Governor Mikhail Yevrayev said Ukrainian drones were attacking the region and temporary restrictions were placed on several roads toward Moscow; he did not comment on refinery damage.
Residents claimed that fires also broke out in some homes in the city after the strike.
Zelensky said the overnight operation was part of what he called "long-range sanctions" meant to limit Russian oil revenue used for the war.
The Yaroslavl refinery is one of Russia's five largest, processing about 15 million metric tons of crude oil per year and producing petrol, diesel, jet fuel, liquefied gas, and fuel oil.
Ukraine has said its campaign against Russian oil infrastructure has forced several refineries to cut output or temporarily halt operations, worsening fuel supply strains across Russia.