MOSCOW (Reuters) -A fire on Sunday at an oil refinery owned by Lukoil near Ukhta in Russia’s northwestern Komi Republic caused fatalities, authorities said, but did not say how many.

Vladimir Uiba, head of the Komi Republic, said the fire had been caused by a failure to comply with safety rules and not by drone attacks that have been seen at some Russian refineries since the war with Ukraine.

The Komi Republic’s Investigative Committee opened a criminal investigation and said that the fire had resulted in deaths and injuries, without giving any numbers.

The emergencies ministry’s regional branch had earlier said three people had been injured. It said 74 of its staff were working to extinguish the fire, which occurred in a tank at the refinery, four kilometres (2.5 miles) from the city of Ukhta.

“According to revised data, it was established that a fire occurred during routine technical works by a contracting company,” the ministry said.

Lukoil had no immediate comment. The refinery’s press service said the plant was operating normally.

It said three employees of Centre Test, the contracting company conducting repair works, had been injured, without giving details.

“I would like to immediately reassure the residents of Ukhta and Komi – the fire is not connected with attacks by enemy drones,” Uiba wrote on Telegram.

Several Russian oil facilities have had to contend with outbreaks of fires in recent months. Some were caused by drone attacks from Ukraine, adding to uncertainty in global oil and gas markets which were already jittery due to the conflict in the Middle East.

Russia and Ukraine have both used drones to strike critical infrastructure, military installations and troop concentrations in their more than two-year conflict.

(Reporting by Reuters; Writing by Alexander Marrow; Editing by Frances Kerry, Hugh Lawson and Susan Fenton)