
Matthew Sussex, a Russia expert and associate professor at the Australian National University, has spoken to BBC News about why Islamic State would attack Russia - and what Moscow would do in response. "Russia has a long history of treating many people on its territory, who are Muslims, not particularly well," he said.
“We've had two wars in Chechnya... the second one 1999-2006 was something like a radicalized war in which you had people who continued to fight with the Islamic State against the Russian government. Since then, Russia's activities in Syria have made the Islamic State view the Russian government as a primary threat."
He says he expects the Russian response to the Crocus Hall attack to be one of "extreme violence," citing the aftermath of the 2002 Moscow theater siege and the 2004 Beslan school siege as examples.
"Perhaps it's not so important who carried out the attacks, but who the Russian government decides is to blame and who they will respond to."
He says the US warning of a possible attack, issued on March 7, was treated by the Kremlin as an attempt to "interfere" in its recent general election and its internal affairs.