Russia said three servicemen were killed at its Engels air base by debris from a Ukrainian drone it said it shot down.
Officials said no Russian aircraft were damaged, but the incident raises questions about the effectiveness of Moscow's air defence.
The Engels base is located more than 600 kilometres east of the Ukrainian border in the Saratov region.
Air force officials in Ukraine have not claimed responsibility for the drones but said the incident was a consequence of Russia’s aggression.
The Engels base is home to long-range strategic bombers that may have been used to carry out missile strikes on various targets in Ukraine.
For more watch Euronews' report in the video above.