40 dead and more than a hundred wounded in Moscow's Crocus City Hall.
Early reports indicate there was a shootout with at least three men wearing combat fatigues entering the concert hall while a progressive rock band was playing, followed by an incendiary bomb/grenade explosion and a fire.
Zelensky and FRL deny being behind it (and I don't see them greenlighting it - they both know terrorist-like actions like this are guaranteed to lose them international support; continuing the drone attacks on oil refineries is more than enough to sting Russia in her wallet and hold up the premise of a would-be, "clean surgical war" with clear rules of engagement), but you can bet Putin and his cronies will milk the tragedy for all it's worth and give it an outrageous spin that'll, in one way or another, pin the blame on every nation west of St Petersburg.
Hell, for all we know, it could be Chechens again...
EDIT: at this time, the primary suspects are Islamic State agents. There
was an advisory from the US embassy in Moscow for US citizens to avoid concert venues, earlier this month, because there were rumors of a planned attack, but the Russian government dismissed it as "cheap provocation".
EDIT two: apparently IS just claimed responsibility for the attack on Telegram.