Several assailants, reportedly linked to ISIL, have been killed in the operation to rescue two guards at a Rostov-on-Don detention centre.

The two guards were taken hostage by six detainees earlier on Sunday, the prison service said, before an operation was launched to free them, Russian media reported.

Initially, the prison service said it had entered into negotiations for the guards’ release. But a short time later it issued a statement saying the siege had ended.

“The criminals were eliminated,” Russia’s Federal Penitentiary Service said in a statement, which added that a “special operation” had taken place to free the hostages, who were not injured.

The hostage-takers reportedly had links to the ISIL (ISIS) group, Russian media reported quoting police sources.

RT reported that three of the hostage-takers had already been sentenced on “terrorism” charges, including disseminating extremist information and plotting to blow up a Russian courthouse.

Journalists on the scene reported the sounds of gunfire, while multiple ambulances were seen arriving at the prison in footage on social media.

Images posted on social media appeared to show at least two of the hostage-takers wearing a headband that resembled the ISIL flag. Other images showed prisoners wielding knives.

The attackers had knocked out the bars of a window in their cell and entered a guard room where they took at least two prison officers hostage, local media said.

Earlier, Russian state news agency TASS, quoting unnamed sources in law enforcement, had said that six hostage-takers were in the central courtyard of the Rostov-on-Don region’s Detention Center No 1, armed with a penknife, a rubber baton and a fire axe.

“The employees who were being held hostage were released. They are uninjured,” the prison service later said.

The Interfax news agency said the hostage-takers demanded to be provided with a car and be allowed to leave the prison in exchange for the release of the hostages.

It was not immediately clear how many of the six hostage-takers had been killed.

The incident comes nearly three months after gunmen killed at least 144 when they opened fire at a concert hall near Moscow in the deadliest attack on Russian soil since the Beslan massacre a decade ago.

Hundreds more were injured.

More than 20 people have since been arrested, including the four suspected attackers, all from the former Soviet republic of Tajikistan. ISIL claimed responsibility for the attack.