A Ukrainian drone is said to have struck an airbase deep inside Russia, while the Kremlin claims to have shot it down and taken it off-course, Three Russian servicemen were killed as a result of the strike.
This is the second time the Engels airbase, hundreds of kilometres away from the border with Ukraine, has been targeted this month, raising questions about the effectiveness of Russia's air defences if drones can fly that far into the country.
Russia's Defence Ministry said the incident took place in the early hours of Monday, and three servicemen were killed by debris at the Engels airbase that houses the Tu-95 and Tu-160 nuclear-capable strategic bombers that have been involved in launching strikes on Ukraine.
Engels is located in Russia's Saratov region on the Volga river, more than 600km east of the Ukraine border.
No damage was inflicted on Russian aircraft, the ministry said.
Euronews could not independently confirm Moscow's claims.
Ukrainian Air Force spokesperson Yurii Ihnat, speaking to Ukrainian television on Monday, did not directly acknowledge his country's involvement in Monday's incident but said: "These are the consequences of Russian aggression."
"If the Russians thought that the war would not affect them in the deep rear, they were deeply mistaken," Inhat added.
Ukrainian officials have never confirmed sending drones into Russia. They have maintained ambiguity over previous high-profile attacks, including drone strikes on Russian military bases earlier this month.
On 5 December, unprecedented drone strikes on Engels and the Dyagilevo base in the Ryazan region in western Russia killed a total of three servicemen and wounded four more.
The strikes on the airbases were followed by a massive retaliatory missile barrage in Ukraine that struck homes and buildings and killed civilians.