Snipers from Russia's National Guard today killed four inmates who had stabbed four prison guards to death and briefly held others as hostages while declaring allegiance to the Islamic State group.
The Federal Prison Service said that four inmates took eight prison guards and four inmates hostage.
It said they stabbed four of the guards, three of whom died on the spot and the fourth one later died at a hospital.
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The agency said three other guards were hospitalised with injuries.
Russia's National Guard said its snipers "neutralised" all four attackers, freeing all the hostages, while the Federal Prison Service also claimed credit for killing the assailants.
The discrepancy couldn't be immediately explained.
Details of the violence at the prison in Surovkino in the Volgograd region, 860km southeast of Moscow, were sparse and it was not clear how the inmates had taken hostages several hours earlier.
Videos that purportedly came from the scene and circulated on Russian media and messaging app channels showed men wielding knives inside and in a prison yard and several men in what appeared to be guard uniforms lying in blood on the ground.
In the videos, the alleged attackers claimed support for the Islamic State group and for the suspects arrested in the March terrorist attack on a Moscow concert hall that left 145 people dead.
An IS affiliate claimed responsibility for that attack, in which gunmen killed patrons waiting for a popular music group to perform and set the building on fire.
The state news agency Tass said court records showed that the hostage-takers were from former Soviet Central Asian countries; all the concert hall attack suspects are from Tajikistan.
