Ukraine's armed forces say they have struck some of Russia's most advanced combat aircraft 1,060 miles inside Russian territory, in one of the deepest drone attacks of the war.
Drones hit Su-57 stealth fighters and Su-34 bombers at Shagol airbase in the Chelyabinsk region, said Kyiv military sources.
The strikes occurred on 25 April although Ukraine is still assessing the damage.
Each Su-57 is worth around £30 million, and the Su-34 about £27 million.
The strike against Vladimir Putin's most modern warplanes - far beyond the Ural Mountains - is a first for Ukraine, if confirmed.
Moscow has said nothing about any such losses.
Regional governor Alexey Teksler described the incident that day only as an 'attempted UAV attack' that was 'thwarted,' insisting there were no casualties or damage.
But Russia often lies about damage to its military equipment.
Local social media posts described drones flying over residential areas at dawn, followed by explosions near the Chelyabinsk Higher Military Aviation School of Navigators, a key training hub for Russia's long-range and drone operators.
Ukraine's armed forces say they have struck some of Russia's most advanced combat aircraft 1,060 miles inside Russian territory, in one of the deepest drone attacks of the war
Drones hit Su-57 stealth fighters and Su-34 bombers at Shagol airbase in the Chelyabinsk region, said Kyiv military sources
The strikes occurred on 25 April although Ukraine is still assessing the damage. Each Su-57 is worth around £30 million, and the Su-34 about £27 million
They said there had been damage.
'It's really frightening,' said one report at the time.
Residents told of windows shaking, car alarms triggering, and smoke rising near the airfield.
Reports indicated damage to hangars and training facilities, with hospitals switching to emergency regimes.
It comes after in January Ukrainian drones wiped out 15 of Vladimir Putin's military aircraft on Russian airfields deep behind the front lines following Operation Spiderweb.
Dramatic footage showed drones successfully striking the planes across five different military bases, although Ukraine has not indicated exactly when the attack took place.
Ukraine's spy service, the SBU, claimed to have taken out 11 Sukhoi and MiG fighter jets, three helicopters and an Antonov An-26 cargo plane.
It said that these aircraft were worth more than $1billion.
The SBU said its top Alpha unit was behind the strikes. Su-30SM and Su-34 jets, some of the Kremlin's most important frontline planes, were destroyed alongside older Su-27 and Su-24 planes, which are used to hit Ukraine.
Ukraine also destroyed MiG-31 interceptors. These are a key part of Russia's air defence system, and are often used to launch hypersonic Kinzhal missiles.
The three choppers - a Mi-8, a Mi-26 and a Mi-28 - will have hurt Russia's transport and logistics capabilities.
The SBU added that fuel and ammo depots were also destroyed in the operation.