know did not. and he is warning of a grave escalation. now, the u.s. has come close to retaliating against iran in the past. if you'll remember, there were those strikes against oil tankers in the persian gulf. then iran's downing of a u.s. drone. america, however, did restrain itself on those occasions. in this case, these particular attacks were in response to an attack outside of kirkok that ended up killing one u.s. contractor. of course the great concern in all of this is that if this situation escalates, that is detrimental not just to the stability of iraq but the region as a whole. >> arwa, thank you very much. and the broader picture here in the stability of the region is critical. let's talk to cnn military and diplomatic analyst john kirby.