Moscow (AFP) - At least 15 people, including 11 children, were killed when a gunman opened fire at a school in the central Russian city of Izhevsk on Monday, with President Vladimir Putin denouncing an "inhuman terrorist attack".

"The president deeply regrets the deaths of adults and children in this school, where a terrorist attack took place," Kremlin spokesman Dmitry Peskov told reporters.

"After the crime, 15 people died, including 11 children and four adults, and there were 24 more injured, including 22 children and two adults," the Investigative Committee of Russia said in a statement Monday afternoon.

"The president wishes recovery to those injured in this inhumane attack," the Kremlin added.

Investigators reported that the suspect, who committed suicide, "was wearing a black shirt with Nazi symbols and a mask."

In a separate statement, they confirmed that the shooter was "a former schoolboy named Artyom Kazantsev, born in 1988." "We are conducting an investigation to see if he is a follower of neo-fascism and Nazi ideology," they added.

Investigators released a video showing the body of a man lying on the ground, with blood around his head, and wearing a black shirt with a red swastika on it.

The Russian Interior Ministry had previously reported six dead and 20 wounded.

"Police officers found the body of the shooter. According to our information, he committed suicide," the ministry said.

The shooting took place in the morning at School No. 88 in the city of Izhevsk, located west of the Ural mountain range separating European and Asian Russia.

This city still includes factories for Kalashnikov assault rifles.

The district governor, Alexander Brechalov, said the attacker "killed a security guard" before opening fire inside the school.

The school's website indicates that it has about a thousand students and 80 teachers.

"The evacuation operation has ended," Brechalov added in a video from outside the school, and "the entire area has been sealed off," explaining that the Russian National Guard, security services and "authorities responsible for the investigation" are at the site. Behind him, medical staff appeared to enter the building in a hurry, some of them carrying a stretcher.

The Ministry of Health confirmed the deployment of "14 ambulance teams" at the site, and a "group of doctors" is scheduled to go to Izhevsk soon to "help the victims."

An investigation was immediately opened on charges of "murder" and "illegal possession of weapons" and entrusted to the Russian Investigative Committee, the country's main investigative body.

The shooting took place on Monday amid tense atmospheres in several regions of Russia, against the background of military mobilization and the call-up of hundreds of thousands of reservists to fight in Ukraine.

A soldier supervising a recruitment center in the Russian army was also seriously injured on Monday, when a man opened fire at the center in Siberia.

The number of bloody shootings has been increasing in Russia, especially in schools, for a few years, after it was so rare that it raises the concern of President Vladimir Putin, who considered it an imported phenomenon from the United States and a negative effect of globalization, which prompted him to tighten the laws on carrying weapons.

And in April, a man shot dead two children and a teacher in a kindergarten before taking his own life, also in the Ulyanovsk region in central Russia.

The country's deadliest shooting occurred in October 2018, when a student killed 19 people at a high school in Kerch, in Russian-annexed Crimea, before taking his own life.

Izhevsk has a population of 650,000 and is the capital of the Udmurt Republic in the center of the country.

It was in this industrial city that was long closed to foreigners during the Communist era that Mikhail Kalashnikov developed the first AK-47 in 1947, and it has become world famous ever since.