Popular rock band Piknik, who were due to perform Friday at Crocus City Hall, on the outskirts of Moscow, where gunmen killed 137 people, paid tribute to the victims of the terror attack.

On Sunday night, members of the Russian band laid flowers outside the building where the bloodbath took place, offering their condolences to the victims’ families after observing a minute’s silence, TASS news agency reported.

“This atrocity is a senseless, unimaginable barbarity,” said group leader Edmund Skliarski.

The fate of a band technician is unknown after the terrorist attack on the concert hall. The armed attackers opened fire indiscriminately on the spectators and caused a fire, which spread rapidly, in an attempt to cause as many casualties as possible.

The Islamic State group claimed responsibility for the attack.

Russian President Vladimir Putin claimed, without providing evidence, that some in Ukraine had made preparations to help terrorists cross the Russian border. Kiev has denied any involvement in the attack.