A terrorist attack at a concert venue outside Moscow left at least 137 people dead and over 180 injured, Russia's deadliest such attack since the Beslan school siege in 2004. Four gunmen opened fire and detonated explosives at the Crocus City Hall as a rock concert was about to begin, causing a horrific fire. While the Islamic State claimed responsibility, suggesting ISIS-K involvement, Russian President Vladimir Putin hinted at potential Ukrainian links despite Kyiv's denial. The tragedy exposed security lapses and dealt a political blow to Putin during the ongoing war in Ukraine.

What we know after the Islamic State group claims responsibility for Moscow massacre | AP News

Putin vows to punish those behind Russia concert massacre | Reuters

Security Questions Emerge as First Charges Are Filed in Russia Attack | NYT