Russian media named the attackers as Ramzidin Toshev, 28, Rustamchon Navruzi, 23, Nazirchon Toshov, 28, and Temur Khusinov, 29. All were from Uzbekistan and Tajikistan.
In a dramatic mobile phone video released by the attackers, they identified themselves as Islamic State militants and said they were motivated by a desire to seek revenge for the persecution of Muslims.
The footage showed prison officials lying in pools of blood, while separate footage showed the attackers running around the prison courtyard.
Volgograd Governor Andrei Bocharov previously said the hostage taking “did not pose any threat to civilians.”
President Vladimir Putin was captured on video attending a virtual meeting with security chiefs, during which the Kremlin said he was given an update on the situation.
The Volgograd hostage crisis was the second this summer, following the kidnapping of two guards at a facility in the nearby Rostov region by six detainees who had pledged allegiance to the Islamic State.
Five prisoners were killed after the attack and a sixth was sentenced to 20 years in prison.
Prosecutors said they had filed a case in connection with the hostage taking.
IK-19 Surovikino is a high-security prison. It is estimated to hold about 1,200 prisoners.
