The attacks come after IS fighters in March killed 145 people in Moscow. (Representational)
Russian inmates on Friday took staff hostage at a prison colony in the southern Volgograd region, officials said, the second such incident in a Russian jail since June.
"Convicts took hostage employees of the (IK-19) correctional institution. Measures are currently being taken to free the hostages. There are casualties," Russia's federal penitentiary service said in a statement.
Russia's investigative committee said "several prisoners" were involved.
Videos published on Russian social media appeared to show around four prison guards taken hostage, some covered in blood.
AFP could not verify those images.
The IK-19 prison colony is located in the town of Surovikino, around 850 kilometres (530 miles) south of Moscow.
The incident happened during a meeting of the prison's disciplinary commission, the federal penitentiary service added.
Elsewhere in June, prisoners aligned with the Islamic State (IS) group staged a seige at a jail in the southern Rostov region.
Russian special forces managed to kill the hostage-takers and freed the guards after an hours-long stand-off.
Officials provided no further information on Friday's incident, who the hostage-takers were or any demands they were making.
The attacks come after IS fighters in March killed 145 people at a concert hall in Moscow in the most deadly terror attack in Russia for two decades.
IS has repeatedly pledged to target Russia over its support of Syrian leader Bashar al-Assad, who has waged a military campaign to quash the group in the Middle East.
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