The drone was shot down early Monday morning, and according to Russian authorities, the three deceased servicemen were hit by debris from the downed drone.
"As a result of falling debris, three military employees from the airfield's technical staff were mortally wounded," writes the Tass news agency.
According to the Russian Ministry of Defense, no aircraft have been damaged.
The drone strike is the second alleged attack in a month against the Engels Air Base, which is located in the Saratov region about 60 miles from the border with Ukraine.
"Consequences of Russian aggression"
Ukraine's air force has neither confirmed nor denied involvement in the attack on the Russian military base.
- These are consequences of the Russian aggression, says Yuriy Ignat, spokesperson for the Ukrainian Air Force, in a televised interview.
- If the Russians thought that the war would not affect them behind the front line, they were thoroughly mistaken.
Strategically important airbase
Russia is believed to have its nuclear-capable strategic bombers stationed at the Engels base.
After the reported attacks on the air base on December 5, Russian President Vladimir Putin promised to strengthen the protection of strategic sites.
The state-run Ukrainian news agency Ukrinform also reports that explosions were heard at the airfield.
Ukrinform neither confirms nor denies that the drone has been sent by the Ukrainian military, but states that "the air base is used for massive robot attacks against Ukraine".