A flurry of gunfire and explosions sent shockwaves through central Chelyabinsk on Thursday morning, news agency Ura.ru reported.
Plumes of smoke enveloped the headquarters of Chelyabinsk's local Federal Security Service branch.
It was later revealed that the local FSB branch was conducting drills as part of an inspection of the building's security.
Special devisions of the FSB as well as armored personnel vehicles participated in the exercise.
"We are currently working on a plan on how to defend our headquarters in case it is captured by terrorist groups. The drills were planned before and the public was notified," head of the Chelyabinsk region FSB Stanislav Neginsky told the Pervy Oblasnoi TV channel.