Ukraine fired more than 40 drones into Russia’s bordering Rostov region, Moscow defense officials said Friday, in what appeared to be one of its biggest air attacks in the war and as Kyiv's forces step up their assaults on Russian soil.

Russia’s Defense Ministry said a total of 44 drones were “intercepted and destroyed” in the Morozovsky district, more than 100 kilometers (60 miles) from the border. The attack damaged a power substation, Rostov Gov. Vasily Golubev said.

Russian media reported that there is a military airfield near the town of Morozovsk, but it was unclear whether the airfield was the target of the attack.

The Russian defense ministry said nine more drones were intercepted over Russia’s border regions of Kursk, Belgorod, Krasnodar and the nearby Saratov region.

Ukrainian officials rarely comment on such strikes and provided no immediate response.

Drone warfare is a key feature of the war, which has extended into a third year since Russia’s full-scale invasion of its neighbor. On the 1,000-kilometer (600-mile) front line, where fighting is largely bogged down, low-cost drones are used by both sides to knock out expensive military hardware.

The Kremlin’s forces have used large numbers of Iranian-designed Shahed drones to bombard urban areas of Ukraine. Kyiv, in turn, has developed small but fast-growing defense industry where drones, including deadly unmanned sea vessels, are proving effective.

Russian authorities have long accused Ukraine of launching regular drone attacks on power plants, oil refineries and other targets in western regions of Russia near the border. Last month, Ukraine fired a barrage of 35 drones at such targets, Russia said.

Some attacks have reached deep into Russia, including Moscow and as far as 1,200 kilometers (745 miles) east of Ukraine.

Ukraine cannot match the scale of Russia’s military, however. Last week, Moscow launched a a mass barrage of 99 drones and missiles against Ukraine’s energy infrastructure, hitting regions across the country.

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