The video on the online 66.Ru news portal shows a pair of helicopter gunships buzzing low, with one of them firing a rocket that explodes next to a spectator.
It said that today two people were wounded and two vehicles destroyed in the incident during the Zapad (West) 2017 maneuvers.
It said it happened Sunday or Monday at the Luzhsky range, about 100 kilometre (60 miles) east of the border with Estonia.
The Russian military today acknowledged the video was genuine, but denied it happened Monday. It did not specify when or where the incident in the video took place but said no one was hurt.