Unverified videos shared through Mash, a Telegram news channel with purported links to Russian law enforcement, showed the attackers claiming to be affiliated with the Islamic State.
They said they were taking revenge for the arrest of Islamic terrorists who killed 145 people in an attack on a Moscow concert hall in March – the most deadly terror attack in Russia for two decades.
‘Stab wounds of varying severity’
Photos on Friday showed prison inmates with knives standing above bloodied guards.
“The criminals inflicted stab wounds of varying severity on four employees, three of whom died. Another four who resisted were hospitalised, one of whom died in hospital,” the federal penitentiary service said in a statement.
The authorities had earlier said on Friday afternoon that all those who had been taken hostage had been freed by the Russian national guard’s special forces.
Drug trafficking
Three of the hostage takers had been convicted of drug trafficking, including one from Uzbekistan and two from Tajikistan, according to the state-run Tass news agency. Another, also from Uzbekistan, was serving a sentence for involuntary manslaughter during a fight.
Officials provided no further information on the hostage-takers or their demands, but Mash said they had asked for a helicopter, $2 million and the right to freely leave Russia.
Russian authorities have launched a criminal case in connection with the hostage-taking, a crime punishable by a maximum of life in prison.
Second hostage situation in recent months
It is the second prison hostage situation in southern Russia in recent months, with six prisoners who had pledged allegiance to the Islamic State capturing guards at a detention centre in the nearby Rostov region in June.
Five were killed, while one was later sentenced to 20 years in prison on terrorism charges.
The terror group, with its origins in Iraq and Syria, has repeatedly pledged to target Russia over its support of Syria’s leader, Bashar al-Assad.