NEW DELHI: At least 60 people were killed and over 145 others injured in a deadly attack by unidentified gunmen on Crocus City concert hall in Krasnogorsk suburb in the north of the Russian capital city of Moscow; according to Russian news agencies. 

The attackers dressed in camouflage uniforms entered the building, opened fire and threw a grenade or incendiary bomb; as per reports.

Authorities said a "terrorist" investigation had been started and President Vladimir Putin was receiving "constant" updates on the attack, his spokesman Dmitry Peskov told Russian news agencies.

Moscow mayor Sergei Sobyanin said there had been a "terrible tragedy" at the concert by Russian rock band Piknik and cancelled all public events in the city for the weekend.

Security services quoted by Interfax news agency said between two and five people "wearing tactical uniforms and carrying automatic weapons" opened fire on guards at the entrance and then started shooting at the audience.

ISIS has claimed responsibility for the deadly attack; ABC News reported.

ISIS released a statement claiming their fighters attacked a big gathering for Christians in the Russian Moscow suburb, injuring hundreds and causing major destruction.