Two prison guards at a jail in southern Russia have been freed without harm after they were taken hostage by Islamic State (IS) inmates, with the assailants "liquidated", the country's prison service confirmed on Sunday.

"In the course of a special operation to free hostages in the pre-trial detention center-1 of the Main Directorate of the Russian Federal Penitentiary Service for the Rostov Region, the criminals were eliminated, and the hostages were released and not harmed," the penitentiary service announced in a statement.

Earlier, the prison service said the defendants held in a pre-trial detention center in Rostov took two employees hostage but added that the center was functioning normally and the situation was under control.

A source had told Sputnik that the hostages were taken by six to seven defendants, who were armed with fire axes and rubber truncheons and who demanded transportation and the possibility to leave the detention center.

The source added that negotiations with the defendants to free the hostages were underway.

According to a police source interviewed by the state news agency TASS, IS members who are due to appear in court on terrorism charges were among the hostage takers.

It is noteworthy that on March 22, IS claimed responsibility for a deadly attack that killed at least 144 people when gunmen opened fire at a concert hall near Moscow.