It is still unclear who is responsible for the double bombing of a crowd in the south-eastern Iranian city of Kerman, but whoever is behind the outrage is clearly willing to risk igniting a regional war.
In Washington, officials have been pointing towards the possible role of Islamic State or some affiliated Sunni extremist group, and away from the partnership of Israel and the Iranian rebel group, the Mujahedin-e-Khalq (MeK), who have reportedly been behind previous attacks deep inside Iran.
