The Russian Federal Security Service (FSB) is considering the attack on its Moscow headquarters that killed one employee an "act of terrorism," Russian media reported.

The shooting was committed by a lone gunman, the FSB press service has said, dismissing media reports that the attacker managed to penetrate the premises of the FSB building.

Earlier reports of at least three attackers, storming into the FSB office and engaging into a firefight with the security operatives, turned out to be inaccurate as well.

The FSB confirmed that one of its operatives was killed in the attack. Earlier, Russia’s Health Ministry said two officers were “critically injured” during the shooting – yet it remained unclear whether the deceased is one of them. A total of five people are being treated for injuries following the incident.

While the FSB itself is reportedly treating the incident as an “act of terrorism,” Russia’s Investigative Committee has described it as an “attempted murder of law enforcement officers,” while announcing the launch of a criminal probe.

The shooting occurred in central Moscow late on Thursday in the immediate vicinity of the FSB headquarters and other buildings used by the security service. The incident yielded many videos, showing massive law enforcement presence at the scene, as well as multiple conflicting reports on what exactly happened.

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Official information on the shooting still remains very scarce, the identity and motives of the attacker remain unknown.

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