What is ISIS-K and why has it attacked Russia?

Emergencies workers at the Moscow Crocus City Hall concert venue. Photo: Reuters

Holly Evans
© UK Independent

In the weeks leading up to the tragedy at a Moscow music venue on Friday night, warnings had been relayed to Russia that a terror attack perpetrated by extremists was imminent.

Despite this, it appears their intelligence services were caught unaware when a group of four gunmen opened fire at Crocus City Hall, where 7,000 concertgoers had gathered to watch the progressive rock band Picnic.