Ukraine launched a wave of drones at Russia and the annexed Crimea peninsula overnight, killing two people, including a child, and setting an oil refinery ablaze, officials said Friday.

The attack was Ukraine’s largest aerial offensive in weeks and comes as Russian forces advance along the frontline, making their biggest territorial gains in 18 months as Kyiv struggles with ammunition and manpower shortages.

Russia’s military said it had intercepted or destroyed more than 100 Ukrainian air and sea drones in the south of the country, and over annexed Crimea and Black Sea overnight.

“Fifty-one UAVs were destroyed and intercepted over Crimea, 44 over the Krasnodar region, six over the Belgorod region and one over Kursk region,” it said, adding naval forces destroyed six drone boats.

One drone struck a family driving near the border in Russia’s Belgorod region, killing a mother and her 4-year-old son, the region’s governor Vyacheslav Gladkov said.

“The child was in critical condition. Doctors did everything possible to save him,” he said, but “to much grief, the 4-year-old died in hospital.”

The father was injured but “is in shock” and refused medical help, while the driver of the car was treated for shrapnel wounds to his hands, he added.

Another drone attack caused a fire at a gas station in the village of Bessonovka, but the flames were quickly put out, according to the governor.

In the coastal town of Tuapse in the southern Krasnodar region, two Ukrainian drones hit an oil refinery, sparking a large fire but without causing any casualties, authorities said.

The Russian-controlled port of Sevastopol on the annexed Crimean peninsula suffered a “partial blackout” after debris from downed drones fell on an electrical substation, the city’s Russian-installed governor, Mikhail Razvozhayev, said.

“While restoration work continues, the city will not be able to receive enough energy. There will be isolated blackouts,” he warned, adding that schools would cancel lessons.

Ukraine did not immediately comment but in the past has denied targeting civilians.

The drone wave comes as Russian forces push into Ukraine’s northeast after storming across the border in a fresh offensive last week.

Ukraine has evacuated almost 9,000 civilians from the border area, as Russia advances towards Vovchansk and nearby villages.