Amid ceasefire deal discussions, Ukraine on Thursday struck Engels military airbase with a drone attack in the Saratov region of southwest Russia.
Videos circulating on social media revealed a major blast spreading out from the airfield. The Russian defence ministry said that the air defences had shot down 132 Ukrainian drones targeting Russian regions.
The Engels military airbase holds Russian strategic bombers and also warehouses cruise missiles and glide bombs.
The base is Russia's sole operating location for Tupolev Tu-160, known as 'Blackjack' by NATO. It is a supersonic, variable-sweep wing nuclear-capable heavy strategic bomber and airborne missile platform.
According to regional officials, ten people were injured in the drone attack.
Russia has imposed a state of emergency in the Engels due to the attack.
The Ukrainian attack comes after Russian President Vladimir Putin agreed to cease all attacks on Ukraine's energy infrastructure.