Ukraine has carried out a drone attack against targets in southern Russia and claims to have destroyed six Russian planes at an airbase in Rostov region.
Security sources told BBC Ukrainian eight more aircraft were badly damaged, while 20 service personnel could have been killed or injured.
The Morozovsk base houses Su-27 and Su-34 aircraft used on the front line in Ukraine, the sources said.
There has been no word from Russia on reports of an airfield attack.
The BBC has been unable to independently verify the reports.
However, Russian officials said that more than 40 drones had been aimed at the region, which borders Ukraine.
BBC Russian military analyst Pavel Aksyonov says an attack by so many drones over a short space of time could have overwhelmed air defences.
Meanwhile, three people were killed and 13 wounded in a series of rocket attacks in the Ukrainian city of Zaporizhzhia.
Regional governor Ivan Fedorov said several high-rise blocks and private homes were damaged.
Two missiles struck first, and then - after rescuers and police arrived - three more hit, he added.
Ukrainian media said several journalists were among the injured.
Earlier, Ukraine's air force said that overnight and into Friday, Russia had attacked Odesa and Dnipropetrovsk regions, and the city of Kharkiv, with 13 drones and five missiles.
All the drones were shot down, it said, but energy facilities were damaged in Odesa region, as well as residential buildings in Kharkiv.
Also, Russian troops continued their slow advance in Donetsk region.
Ukrainian officials said the town of Chasiv Yar was coming under constant bombardment amid reports that Russian forces had reached the outskirts.
.@ISIDEWITH2 години2Y
How would you feel if a foreign country used drones to attack your nation's military assets?
@ISIDEWITH2 години2Y
What emotions come up for you when you hear about civilian casualties in conflict zones, even if those casualties are a result of actions taken in a military context?
