The European Court of Human Rights has strongly criticised Russia for failing to take action to prevent the 2004 Beslan school siege in which 330 people died in a Chechen militant attack.
In the siege, Chechen rebels took more than 1,000 hostages, mostly children.
On Thursday morning, the ECHR ruled unanimously that Russia had failed to prevent the attack, despite intelligence services having "specific information of a planned terrorist attack in the area, linked to an educational institution", reported BBC.
The judges also found there were "serious shortcomings" in the security operation to end the siege, which culminated in there not being a single fire engine at the scene when the raid occurred.
And they ruled that the use of tanks, grenade launchers and flame-throwers to break the hostage situation "contributed to the casualties among the hostages" and was not justified in the circumstances.
The case was brought by 409 people, including those injured and taken as hostage in the attack itself, as well as family members of those killed, according to the report.
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Russia said the ruling was "utterly unacceptable" and that it would appeal.
"We cannot agree with such a conclusion in a country that has been a victim of terrorist attacks multiple times," said Kremlin spokesman Dmitry Peskov.
"Unfortunately the list of such countries is growing and is unfortunately growing regularly, so such conclusions for a country that endured an attack are absolutely unacceptable."
The Beslan school siege began when 30 separatist gunmen took more than 1,100 hostages in School Number 1 in September 2004.
Russian special forces stormed the building in a blaze of gunfire after 52 hours, and 334 people, including 186 children, were killed in the hail of bullets, explosions and fire that followed.
Witnesses described the operation by Russian security forces as chaotic, saying that the troops used excessive force and heavy weapons.
According to reports, survivors and relatives say officials, including President Vladimir Putin, mishandled the hostage crisis and ignored intelligence indicating that a hostage-taking scenario was being planned.
A Russian investigation into the events stalled several years ago.