A neo-Nazi gunman killed at least 15 people — including 11 children — in a Russian school on Monday, while wearing a swastika shirt and celebrating the cowardly Columbine school shooters.

Artem Kazantsev, 34, also wounded at least 24 others, all but two of whom were children, before shooting himself dead in a classroom in School No. 88 in Izhevsk, local officials said. 

The mass killer — once a student at the school — was shown lying in a pool of blood, dressed all in black with a red swastika in a circle drawn on his shirt in the attack during Rosh Hashanah.

The weapons found with him had braided keychains that made clear he was inspired by Eric Harris and Dylan Klebold, who killed 13 during a 1999 assault on Columbine High School in Littleton, Colorado.

One had the word “Columbine” in English, while the other had “Eric” and “Dylan,” according to photos shared by the ASTRA news agency.

He also appeared to have several pistol magazines with him, with the word “hatred” scrawled in red, according to the outlet.

Investigators have said two security guards and two teachers were among the victims, adding that the attacker “committed suicide.”

It was not immediately clear how old the child victims were, but the school has children from grades 1 through 11.

Kazantsev had been registered as a patient at a psychiatric facility, according to the governor of Udmurtia, Alexander Brechalov.

According to investigators, the gunman “was wearing a black top with Nazi symbols and a balaclava” and was not carrying any ID.

“Checks are being made into his adherence to neo-fascist views and Nazi ideology,” said Russia’s Investigative Committee, which handles major crimes.

“Currently investigators … are conducting a search of his residence and studying the personality of the attacker, his views and surrounding milieu.”

Kremlin spokesman Dmitry Peskov described it as “a terrorist act by a person who apparently belongs to a neo-fascist organization or group.”

“President [Vladimir ] Putin deeply mourns deaths of people and children in the school, where a terrorist act took place,” Peskov said.

“The president expressed his deepest condolences to all those who lost their loved ones, their children in this tragic incident, and wished the soonest recovery to those wounded in the inhumane terrorist attack,” Peskov said.

One of the gunman’s uncles, Mikhail Kazantsev, also told ASTRA that the killer “was mentally ill, he was being treated.” However, he refused to elaborate.

The attack came just hours after a gunman shot a recruitment officer at an enlistment center in Siberia, leaving him fighting for life.

 The attack came just hours after a gunman shot a recruitment officer at an enlistment center in Siberia, leaving him fighting for life.

In May 2021, a teenage gunman killed seven children and two adults in the city of Kazan. In April 2022, an armed man killed two children and a teacher at a kindergarten in the central Ulyanovsk region before committing suicide.

Russia has seen several school shootings in recent years.

With Post wires