The attack occurred at School No. 88 in Izhevsk, the capital of the Udmurt Republic, a region in central Russia west of the Ural mountains. The head of the Udmurt republic, Alexander Brechalov, said that 23 people were injured — including 20 children.

Russia’s Investigative Committee identified the gunman as Artem Kazantsev, a 34-year-old local resident and former student at the school. Investigators were searching his residence.

Brechalov told reporters that Kazantzev was registered with a psycho-neurological clinic.

The shooting did not appear to be connected with a spate of violence in recent days that followed Russian President Vladimir Putin’s declaration of a partial military mobilization. In one of the latest incidents, a young Russian man on Monday shot the chief of a local military enlistment office in the Irkutsk region of Siberia.

The gunman, clad in black pants, black jacket, the swastika T-shirt, and a black balaclava, shot the school security guard before walking into the school and opening fire on children, many of them as young as 7 years old, according local media accounts.

Panic-stricken children fled the school during the attack, as police with pistols raised rushed up stairwells and along school corridors, according to video aired by independent local media.

Children huddled silently with their teachers in classrooms, according to videos published by local media. In another video, shots could be heard as the children and staff hid.

A seventh-grade boy at the school jumped from a third floor window to escape the shooting and broke his leg, Russian newspaper Moskovsky Komomolets reported.

Ammunition clips piled on a desk next to the gunman’s body in images of the scene published by local media bore the word “hatred” in red paint. Two pistols near his body had braided cords with the words Columbine, Dylan and Eric, a reference to the 1999 Columbine school massacre in which 13 people were killed by Eric Harris and Dylan Klebold.

The Kremlin spokesman, Dmitry Peskov, called the attack “an inhuman act of terrorism” and said Putin was deeply saddened by it. Peskov said the…