According to the sources, fires broke out at two units at the Tyumen oil refinery following the drone attack: a diesel hydrotreatment unit and a high-octane gasoline production unit.
Reuters sources declined to predict when the refinery could resume operations.
Reuters previously reported, citing Russian authorities, that a Ukrainian drone strike caused a fire at the Tyumen oil refinery, located more than 2,000 kilometers from Ukraine.
The refinery has a nominal capacity of about 9 million metric tons of crude oil a year, or 180,000 barrels per day. Market participants estimate that the refinery can process about 6 million metric tons of crude oil annually, producing about 500,000 metric tons of gasoline and 2.8 million metric tons of diesel fuel, Reuters reported.
A drone attack on the Tyumen oil refinery was reported on June 20.
Residents of Tyumen's Antipino district, where the refinery is located, reported hearing at least two powerful explosions.
Journalists from the ASTRA project later analyzed eyewitness video recorded near the facility and confirmed that a thick column of smoke was rising above the refinery.
The same day, President Volodymyr Zelenskyy said the Ukrainian Armed Forces' Special Operations Forces had carried out the strike on the Tyumen oil refinery.
He also said the operation involved new upgraded drones made by Ukrainian company Fire Point that, according to him, can strike targets up to 3,000 kilometers away.
On July 25, the Special Operations Forces said its Deep Strike units, working with the Black Spark resistance movement in Russia, had struck the Tyumen oil refinery again.
According to the Special Operations Forces, the drones traveled more than 2,000 kilometers to reach the target. Key units at the refinery were protected by anti-drone netting, but the defenses failed to prevent the strike, and a fire broke out at the facility.