A Ukrainian drone attack on the Russian city of Nizhnekamsk killed 13 people, including a child, and wounded 75 others on Monday, authorities in Russia's Tatarstan region said.
Ukraine's military said it had struck an oil refinery in the city, while Russian officials described the attack as a "massive" assault targeting industrial and civilian facilities.
The city's press service did not specify what was hit. Nizhnekamsk is an important oil refining hub, home to two refineries and a petrochemical plant.
Ukraine's General Staff said its forces struck the Taneco oil refinery, causing a fire. The claims could not be independently verified.
Ukraine has increasingly targeted Russian oil facilities with long-range drones in recent months. The attacks have reduced Russian refining capacity and contributed to fuel shortages in parts of the country.
Ukrainian President Volodymyr Zelenskyy has described the campaign as an effort to pressure Russian President Vladimir Putin to negotiate an end to the war.
Nizhnekamsk is about 1,200 kilometers (750 miles) east of the Ukrainian border and has a population of around 240,000.
Ukraine's domestically developed long-range drones have increasingly reached deep into Russian territory, with some attacks reported as far as Siberia, around 2,000 kilometers (1,200 miles) from the border.
"We do deliver entirely justified responses, and every Russian strike will be met with our response. Russia’s war will be felt more and more at their own home – in Russia," Zelenskyy said Sunday on social media.
"The only reason this is still continuing is Russia’s unwillingness to end this war."
Russia has also continued its regular air attacks on Ukraine using missiles, glide bombs and drones, striking civilian areas and causing thousands of civilian casualties, according to the United Nations.
The World Health Organization's European office said Monday that one of its warehouses in Ukraine's central Dnipro region had been struck twice in less than 24 hours.
The attacks destroyed emergency medical supplies worth an estimated $500,000 that were intended for frontline health facilities. No casualties were reported.
