Russia's Saratov oil refinery stopped oil processing on Wednesday following damage from a drone attack, two sources with knowledge of the matter told Reuters.
Ukraine has increased attacks on Russia's energy infrastructure in recent months to try to undermine Moscow's war effort.
The attacks have resulted in fuel shortages in Russia, leading to long queues at filling stations, increased fuel prices and fuel exports curbs.
Read more: Ukrainian drones batter Russian oil facilities and set more oil tankers ablaze
Earlier this week, Omsk oil refinery, Russia's largest, also halted operations following a Ukrainian drone attack.
On Wednesday, Saratov regional governor Roman Busargin said on Telegram that a strike had killed one person, wounded several others and damaged what he referred to as "civilian industrial sites". He did not name the sites, while Ukraine's military said it had struck Saratov refinery.
According to the sources, drones hit the primary refining unit, CDU-6, with a capacity of 20,000 metric tons per day, the only such unit at the refinery.
Owner Rosneft did not respond to a request for comment.
Fuel from the Saratov refinery has not been offered on the St Petersburg International Mercantile Exchange since Wednesday, exchange data showed.
Read more: India's Russian oil imports rise in May as refiners boost purchases
The refinery also suspended operations after drone attacks in March and May.
In 2024, the plant processed 5.8 million tons of oil, or 2.2% of Russia's total refining, producing 1.2 million tons of gasoline, 1.9 million tons of diesel and 1.0 million tons of fuel oil.
