Authorities have detained eleven individuals in connection with the attack, with four directly involved in the assault, according to Russia`s Federal Security Service.

Videos circulated online depict gunmen shooting civilians at close range inside the venue, with a subsequent fire leading to the collapse of the theatre`s roof.

The Islamic State group claimed responsibility for the attack, although neither the Kremlin nor Russian security services have officially attributed blame. However, US intelligence agencies have confirmed IS involvement.

The UN Security Council condemned the attack as "heinous and cowardly terrorism," emphasizing the need for accountability for the perpetrators.

Messages of outrage and support have poured in from around the world, with expressions of solidarity and condolences for the victims and their families.

In the wake of the tragedy, hundreds of people in Moscow queued to donate blood and plasma, demonstrating solidarity and community support in the face of adversity.

The attack has raised concerns about security measures in Russia, particularly in the aftermath of President Putin`s recent electoral victory and amid ongoing conflicts, such as the situation in Ukraine.

President Putin denounced Western warnings of potential terrorist attacks as attempts to intimidate Russians.

This incident marks one of the deadliest attacks in Russia since the downing of a passenger plane over Sinai in 2015 by the Islamic State, highlighting the persistent threat of terrorism in the region.

Meanwhile, in Moscow hundreds of people stood in line on Saturday morning to donate blood and plasma, Russia`s health ministry said.

The UN Security Council condemned "the heinous and cowardly terrorist attack" and UN Secretary-General Antonio Guterres also condemned the terrorist attack.