A “massive” Ukrainian drone strike on an industrial city deep inside Russia killed at least 13 people, according to the local mayor, as Kyiv steps up its campaign of long-range strikes on targets far from the frontline.

Kyiv said it hit the Taneko refinery in the industrial city of Nizhnekamsk, around 1,200km (750 miles) from the Ukrainian border. The raid was part of a campaign to reduce the “military potential of the Russian aggressor,” Ukraine’s general staff said. Footage circulating online appeared to show smoke rising from the refinery in the city.

Russian investigators claimed civilian and industrial sites in the city had been hit. The head of Tatarstan, Rustam Minnikhanov, said a Ukrainian drone hit a hostel, killing nine people. He posted images showing a badly damaged building.

If the death toll is confirmed, the strike would be among the deadliest Ukrainian attacks on Russian territory since the full-scale invasion began in 2022, underscoring the growing reach of Kyiv’s strikes deep inside Russia.

The Uzbek consulate said seven of the victims were Uzbek citizens, who had died as a result of a “terrible incident”. Minnikhanov declared a day of mourning, as Russian prosecutors opened a criminal case into alleged “terrorism”.

Local video footage shows Ukrainian drones buzzing above the city’s skyline, flying low over grey and box-like Soviet-era apartment blocks. Two plumes of black smoke can be seen rising above an industrial zone on the wooded outskirts of Nizhnekamsk.

The site is home to Taneko, one of Russia’s biggest and most technologically advanced oil refineries, owned by the firm Tatneft. It also houses a plant that produces rubber and petrochemical products. Ukraine has bombed the area before, hitting it in June.

In an address on Sunday, Volodymyr Zelenskyy said “long-range sanctions” against the Kremlin and its war machine would continue. In recent months Ukrainian drones have wreaked havoc on Russia’s oil export industry, hitting refineries, including in Siberia, 2,500km away from the frontline.

Speaking on Monday, the governor of the Tyumen region in western Siberia said several Ukrainian drones had fallen on an industrial facility. Emergency services were dealing with a fire, he added.

There have been multiple strikes on warehouses belonging to Wildberries, Russia’s equivalent of Amazon, as well as on oil tankers in the Sea of Azov and Black Sea. Ukraine’s long-term goal is to slowly strangle the Russian economy, so Moscow can no longer fund its war.

Zelenskyy described his country’s remote bombing campaign as “entirely justified”. “Every Russian strike [on Ukrainian towns and cities] will be met with our response. Russia’s war will be felt more and more at their own home – in Russia,” he said on social media.

He added: “The only reason this is still continuing is Russia’s unwillingness to end this war.”

Russia’s defence ministry said it had intercepted 456 Ukrainian drones flying above Russian territory and annexed Crimea. Ukraine says it is knocking out its opponent’s air defence systems more quickly than they can be replaced, creating air corridors or “doors” it can exploit.

Overnight Ukraine’s armed forces hit equipment depots and a repair unit in the occupied Donetsk and Luhansk parts of eastern Ukraine. There were unconfirmed reports Russian ballistic missile launcher systems were destroyed inside Russia, not far from the border.

According to Telegram channels, citing Ukrainian military sources, the targeted high-value military assets were in Russia’s western Kursk and Bryansk regions. Both were used to launch Iskander and hypersonic Zircon missiles towards Kyiv.

Ukrainian prosecutors, meanwhile, said five people were killed on Sunday in a Russian artillery strike on a village outside the north-eastern city of Kharkiv. Several houses were flattened as a result of an “enemy strike” on Bugaivka in the Chuguiv district, they said.