No, but I'm pretty sure they're not the only authority allowed to do that or to charge people with crimes against humanity.
The US has a supreme court case where some torturers (Who tortured people in south america) were held to be under "Universal jurisdiction" and "Hostis humani generis" (Enemies of all mankind), and thus it was irrelevant who they were or where they did the crime, any nation with them in their borders had a positive duty to prosecute them.
I'd argue that joining ISIS has made her hostis humani generis and universal jurisdiction applies to terrorists in the same way it does slavers, torturers, pirates, and war criminals.
https://en.wikipedia.org/wiki/Hostis_hu ... f_the_term