The Novocherkassk, a large landing ship, was “destroyed”, the air force said on the Telegram messaging platform on Tuesday.
People say that it transported drones, the message added.
The air force did not identify the location of the attack, but commander Mykola Oleshchuk posted a video of an explosion at the Russian naval base of Feodosia, on the Black Sea in Crimea, and said the Novocherkassk had been hit.
Russia seized and then annexed the peninsula from Ukraine in 2014.
“And the fleet in Russia is getting smaller and smaller! Thanks to the Air Force pilots and everyone involved for the filigree work!” Oleshchuk wrote without providing evidence.
Sergey Aksyonov, the Moscow-installed governor of Crimea, acknowledged Feodosia had been hit and said the attack had triggered a fire that had been brought under control: “An enemy attack was carried out in the area of Feodosia.”
“The port area is cordoned off,” he wrote on Telegram.
Footage shared by several Russian news outlets on Telegram showed powerful explosions and fires over a port area.
Ukraine and Russia have often exaggerated the losses they claim to have inflicted on the other since Russia launched its full-scale invasion of Ukraine in February 2022.
They have also underplayed their own casualty and equipment losses.
In recent days, Moscow has claimed to have taken control of the eastern city of Maryinka, with Kyiv denying that it has.
Kyiv and Moscow have also each claimed success in shooting down the other’s fighter planes, with each side denying any losses.
In April 2022, Ukraine sank the cruiser Moskva, the Soviet-era flagship of Russia’s Black Sea Fleet.
Moscow announced “a detonation of ammunition” triggered a fire and forced the crew to evacuate, and the ship sank as it was being towed to port.
