The flag shown being held by hostages against the window of Lindt Chocolat Cafe is not an Islamic State flag, but is an Islamic flag that has been co-opted by jihadist groups.

However, Greg Barton, a terrorism expert from Melbourne's Monash University, said that "getting hold of an [Islamic State] flag would be quite difficult, and people will make do with what they have got".

That means it doesn't help confirm or rule out that the hostage-takers' affiliation is with Islamic State or any other group.