Russian snipers have killed four armed prisoners who seized guards at a jail and declared allegiance to the Islamic State, according to local media reports.
The National Guard Service said the inmates were "neutralised" and all hostages freed, though the number was not specified, the reports said.
Earlier, the Russian website Mash showed a video of at least two attackers, with one declaring they were "mujahideen" and saying they had taken over the prison.
Four uniformed officials could be seen in pools of blood - three of them motionless. Another was sitting upright in a doorway with a knife held to his neck.
Other videos showed four men pacing about a prison yard where a bloodied prison staff member was being held hostage.
One of the prisoners appeared to have an improvised explosive vest while the others were carrying knives and hammers.
Before the inmates were shot state news agency Tass said four victims had been taken to hospital, with two of them in serious condition.
Unconfirmed reports on the Telegram messaging app said one or two people had died.
The violence occurred on Friday at a penal colony, believed to be IK-19 in Surovikino, southwestern Russia.
"During a session of a disciplinary commission, convicts took staff of the penal institution as hostages," said a prison service statement.
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Russian news sites published the names of four alleged attackers and said they were from Uzbekistan and Tajikistan, but there has been no official confirmation.
President Vladimir Putin was later recorded at a security council meeting asking leaders for an assessment of the situation.
The prison involved can hold more than 1,200 male inmates and is classed as a "harsh regime" penal colony.
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Tap hereThis year has seen a number of Islamist militant attacks in Russia.
The worst was in March when more than 140 people died after gunmen attacked a concert hall near Moscow and set the building on fire.
Special forces also shot dead six people involved in an IS-linked prison uprising in June in the southern Rostov region.
At least 20 were killed in the same month in shootings in Dagestan, a predominately Muslim region also located in southern Russia.
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