Snipers from Russia’s national guard on Friday killed four inmates who had seized prison guards as hostages and declared allegiance to the Islamic State group, Russian media reports said.

The National Guard Service said the rebellious inmates were “neutralized” and all the hostages had been freed, although the number of hostages was not immediately specified, the reports said.

Details of the violence at the prison in Surovkino, 535 miles southeast of Moscow, were sparse and it was not clear how the inmates had taken hostages several hours earlier.

Before the inmates were shot, state news agency Tass said four victims were taken to a local hospital and two of them were in serious condition. Unconfirmed reports on Telegram messaging channels said one or two people died.

Russian news site Meduza posted a video that it said was from the scene, showing 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 video, 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.

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.

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