Authorities say inmates have taken hostages at a remote prison in the Volgograd region of southwestern Russia.
Federal prison authorities said there were “casualties” as a result of the hostage-taking at the IK-19 Surovikino facility, about 120 km (74.5 miles) west of the regional center of Volgograd, but did not specify the number.
One person was killed and four were taken to hospital with injuries, state news agency Tass said.
An unverified image posted on social media shows a knife-wielding prisoner standing over a bloodied prison guard.
Emergency services said three prisoners were involved in the hostage-taking. It is unclear how many hostages were taken.
Authorities say they are preparing to rescue the hostages.
Volgograd region governor Andrei Bocharov said the hostage-taking “poses no threat to civilians”.
The Kremlin said President Vladimir Putin had been informed of the situation.
The Volgograd hostage taking is the second such incident this summer, after Six prisoners took the oath of allegiance The Islamic State group has captured two guards at a facility in the Rostov region.
Five inmates were killed and a sixth was sentenced to 20 years in prison following the attack.
Prosecutors said they have opened a case related to the hostage taking.
IK-19 Surovikino is a high-security prison camp. It is believed to hold around 1,200 prisoners.
