Updated with hostage release.
Two prison guards at a detention center in the southern Russian city of Rostov have been freed unharmed just hours after inmates with connections to the Islamic State took them hostage, Russia's prison service said Sunday.
"During a special operation... the criminals were liquidated and the employees taken hostage were freed and were not injured," the prison service said in a statement.
Prison authorities had said earlier on Sunday that "negotiations on the release of the hostages" were underway.
The state-run TASS news agency, citing an anonymous law enforcement source, reported that IS members who are due to appear in court on terrorism charges were among the hostage takers.
Russia has been the target of several attacks claimed by the militant organization.
On March 22, gunmen killed at least 144 people when they opened fire at a concert hall near Moscow in the deadliest attack on Russian soil in two decades.
More than 20 people have since been arrested in connection to that attack, which was claimed by IS, including the four suspected attackers, all from the former Soviet republic of Tajikistan.
