Russia's Defense Ministry says three people have been injured in an explosion inside an elite military academy in Russia's second-largest city.

The ministry said in a statement on Tuesday that an unidentified "object" went off early afternoon inside the prestigious Mozhaisky Academy in St. Petersburg, which trains officers for the army's missile defense unit. Three people suffered non-life-threatening injuries.

Live footage from outside the academy showed dozens of cadets being led out of the gated compound.

No other details were immediately available.