A fire has broken out at an airport in Russia’s southern Kursk region, which borders Ukraine, following a suspected drone attack.

The fire occurred the day after Moscow blamed Kyiv for drone strikes on two air bases deep inside Russia and launched another wave of missile strikes on Ukrainian territory.

Kursk Governor Roman Starovoy said in a Telegram post: “As a result of a drone attack, an oil reservoir caught on fire in the area of Kursk airport. The fire is being contained. All emergency services are working on the spot.”

Ukrainian officials have not formally confirmed carrying out the attacks.

The unprecedented attacks in Russia threaten a major escalation of the nine-month war. One of the airfields that was hit houses bombers capable of carrying nuclear weapons.

The attacks showed the vulnerability of some of Russia’s most strategic military sites, raising questions about the effectiveness of their air defences if drones could come so close to them.

The ministry did not say where the drones had originated, but Russian military bloggers said they were likely launched by Ukrainian scouts.

The Russian defence ministry said it had shot down two Ukrainian drones. It said three Russian servicemen were killed and four others wounded by debris, and that two aircraft were slightly damaged.

The attacks on the Engels base in the Saratov region on the Volga River and the Dyagilevo base in the Ryazan region in western Russia were part of Ukraine’s efforts to curtail Russia’s long-range bomber force, the ministry said.

The Engels base, located more than 370 miles east of the border with Ukraine, houses the Tu-95 and Tu-160 nuclear-capable strategic bombers that have been involved in launching strikes on Ukraine.

The Dyagilevo air base, which houses tanker aircraft used to refuel other planes in flight, is about 300 miles north-east of the Ukrainian border.