Ukraine launched hundreds of drones at targets deep inside Russia overnight, killing at least 13 people and wounding 48 others in one of Kyiv’s deadliest attacks on Russian territory since the full-scale invasion began more than four years ago, Russian officials said Monday.

The attack struck the city of Nizhnekamsk in Russia’s energy-rich Tatarstan region, more than 1,000 kilometers (620 miles) from the Ukrainian border. The region is home to several major oil-refining facilities that Ukraine has targeted in recent months as both sides have intensified long-range attacks on critical infrastructure.

Radmir Belyayev, the mayor of Nizhnekamsk, said unspecified industrial and civilian facilities were hit in the overnight strikes. Ukraine’s military separately said it had targeted the Taneco oil refinery, reporting that a fire broke out at the facility.

Ukraine has increasingly targeted Russian oil refineries and other energy infrastructure in an effort to disrupt Moscow’s fuel supplies and military logistics. Previous strikes have contributed to fuel shortages in some parts of Russia and reduced the country’s oil-refining capacity.

The Russian Defense Ministry said its forces intercepted or destroyed 456 Ukrainian drones during the overnight attack. The ministry did not specify how many drones reached their intended targets or how many were intercepted over Tatarstan.

Ukraine’s Air Force, meanwhile, said Russia launched 126 drones against Ukraine during the same overnight period.

Ukrainian President Volodymyr Zelenskyy has defended the long-range strikes as a response to Russia’s continued attacks on Ukrainian territory, saying the campaign is intended to pressure Russian President Vladimir Putin to enter negotiations to end the war.

“We do deliver entirely justified responses, and every Russian strike will be met with our response,” Zelenskyy said in a social media post late Sunday. “Russia’s war will be felt more and more at their own home — in Russia.”

The United Nations has warned that the intensification of long-range attacks by both sides has contributed to a rise in civilian casualties in Russia and Ukraine. Russia has repeatedly launched missiles, drones and glide bombs against Ukrainian cities and civilian infrastructure, causing thousands of civilian casualties, according to UN figures.

Meanwhile, fighting continued near the front line in northeastern Ukraine. Ukrainian authorities said a Russian artillery strike on the village of Bugaivka in the Chuhuiv district of the Kharkiv region killed five people.

“On August 10, Russian forces carried out a massive artillery strike on the residential area of the village of Bugaivka,” the regional prosecutor’s office said. Several houses were destroyed in the attack, according to Ukrainian officials.